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Seq	Timestamp	Type	Name	Duration
0/0	2026/10/21 08:12	flow	patch-triage	3m Args: null Results: { "EnableConfigs": [ "KVM", "KVM_INTEL", "KVM_AMD" ], "FocusSymbols": [ "vmx_recalc_lbr_msr_intercepts", "svm_set_lbr_msr_intercepts", "svm_recalc_lbr_msr_intercepts", "svm_update_lbrv", "kvm_vm_ioctl_set_msr_filter", "vmx_recalc_intercepts" ], "KMSANReasoning": "The patch series fixes an issue in KVM where updating userspace MSR filters (via KVM_X86_SET_MSR_FILTER) did not refresh the LBR (Last Branch Record) MSR intercept bitmaps if KVM's internal passthrough tracking state had not changed. It updates SVM and VMX to unconditionally recalculate/refresh LBR MSR intercepts during MSR intercept recalculation.\n\nKMSAN is specialized in detecting reads of uninitialized memory and information leaks to userspace. In this patch series:\n1. No data structures or buffers are copied to userspace (no copy_to_user, put_user, netlink, ioctl return payloads).\n2. No new memory allocations or complex structs are introduced.\n3. The variables and struct fields accessed (such as svm-\u003elbr_msrs_intercepted and lbr_desc-\u003emsr_passthrough) are already initialized during vCPU creation and maintained within vCPU lifecycle.\n4. No bounds checks, buffer lengths, or memory reads/writes of uninitialized buffers are modified.\n\nBecause the changes do not introduce or expose any uninitialized memory accesses or information leaks, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false, "Reasoning": "The patch series updates KVM's MSR intercept recalculation logic for both Intel VMX and AMD SVM to ensure userspace MSR filter changes are reflected for passed-through LBR MSRs. It introduces vmx_recalc_lbr_msr_intercepts() with a new WARN_ON_ONCE assertion, refactors svm_recalc_lbr_msr_intercepts()/svm_set_lbr_msr_intercepts(), and hooks them into intercept recalculation paths triggered by KVM_X86_SET_MSR_FILTER. These changes touch reachable core virtualization code accessible via /dev/kvm ioctls and guest operations.", "WorthFuzzing": true }
1/1	2026/10/21 08:12	action	read-patch-diff	0m Args: null Results: { "PatchDiff": "commit 72ebad61c471673f43782933fb8f29af6aea0363\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Wed Oct 21 08:12:40 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c\nindex fe0cba4731b2e..55b3ee8403654 100644\n--- a/arch/x86/kvm/svm/svm.c\n+++ b/arch/x86/kvm/svm/svm.c\n@@ -721,14 +721,11 @@ void svm_alloc_permissions_map(unsigned long size, gfp_t gfp_mask)\n \treturn pm;\n }\n \n-static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n+static void svm_set_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n {\n \tstruct vcpu_svm svm = to_svm(vcpu);\n \tbool intercept = !(svm-\u003evmcb-\u003econtrol.misc_ctl2 \u0026 SVM_MISC2_ENABLE_V_LBR);\n \n-\tif (intercept == svm-\u003elbr_msrs_intercepted)\n-\t\treturn;\n-\n \tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHFROMIP, MSR_TYPE_RW, intercept);\n \tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHTOIP, MSR_TYPE_RW, intercept);\n \tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTINTFROMIP, MSR_TYPE_RW, intercept);\n@@ -740,6 +737,22 @@ static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n \tsvm-\u003elbr_msrs_intercepted = intercept;\n }\n \n+static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n+{\n+\tstruct vcpu_svm svm = to_svm(vcpu);\n+\tbool intercept = !(svm-\u003evmcb-\u003econtrol.misc_ctl2 \u0026 SVM_MISC2_ENABLE_V_LBR);\n+\n+\t/\n+\t * Skip redundant updates from svm_update_lbrv(), e.g. on every nested\n+\t * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the\n+\t * bitmap unconditionally, as userspace MSR filters may have changed.\n+\t /\n+\tif (intercept == svm-\u003elbr_msrs_intercepted)\n+\t\treturn;\n+\n+\tsvm_set_lbr_msr_intercepts(vcpu);\n+}\n+\n void svm_vcpu_free_msrpm(void msrpm)\n {\n \t__free_pages(virt_to_page(msrpm), get_order(MSRPM_SIZE));\n@@ -795,8 +808,13 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu)\n \tsvm_disable_intercept_for_msr(vcpu, MSR_SYSCALL_MASK, MSR_TYPE_RW);\n #endif\n \n+\t/\n+\t * Unconditionally refresh the LBR MSR intercepts, as userspace MSR\n+\t * filters may have changed, in which case the bitmap may be stale even\n+\t * if KVM's desired interception hasn't changed.\n+\t /\n \tif (lbrv)\n-\t\tsvm_recalc_lbr_msr_intercepts(vcpu);\n+\t\tsvm_set_lbr_msr_intercepts(vcpu);\n \n \tif (cpu_feature_enabled(X86_FEATURE_IBPB))\n \t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W,\ndiff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h\nindex 84f19026d3e8b..62e08d6d4706e 100644\n--- a/arch/x86/kvm/svm/svm.h\n+++ b/arch/x86/kvm/svm/svm.h\n@@ -364,6 +364,12 @@ struct vcpu_svm {\n \n \tbool avic_irq_window;\n \tbool x2avic_msrs_intercepted;\n+\n+\t/\n+\t * True if KVM wants the LBR MSRs to be intercepted. Note, userspace MSR\n+\t * filters may force interception regardless, i.e. this doesn't\n+\t * necessarily reflect the state of the MSR bitmap.\n+\t /\n \tbool lbr_msrs_intercepted;\n \n \t/ Guest GIF value, used when vGIF is not enabled /\ndiff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c\nindex 70a8c48161356..b945213f0b686 100644\n--- a/arch/x86/kvm/vmx/pmu_intel.c\n+++ b/arch/x86/kvm/vmx/pmu_intel.c\n@@ -517,7 +517,8 @@ static void intel_pmu_refresh(struct kvm_vcpu vcpu)\n \tmemset(\u0026lbr_desc-\u003erecords, 0, sizeof(lbr_desc-\u003erecords));\n \n \t/\n-\t Setting passthrough of LBR MSRs is done only in the VM-Entry loop,\n+\t * LBR MSRs are initially passed through only in the VM-Entry loop (a\n+\t * full MSR intercept recalc merely refreshes an existing passthrough),\n \t * and PMU refresh is disallowed after the vCPU has run, i.e. this code\n \t * should never be reached while KVM is passing through MSRs.\n \t /\n@@ -704,6 +705,23 @@ static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n \tlbr_desc-\u003emsr_passthrough = true;\n }\n \n+/\n+ Refresh the LBR MSR intercepts if the LBRs are passed through, so that\n+ * changes to userspace MSR filters are reflected in the MSR bitmap. There's\n+ * nothing to do if the LBRs are intercepted, as a filter can only force\n+ * interception, never prevent it.\n+ /\n+void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n+{\n+\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\n+\n+\tif (WARN_ON_ONCE(!lbr_desc))\n+\t\treturn;\n+\n+\tif (lbr_desc-\u003emsr_passthrough)\n+\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\n+}\n+\n /\n * Higher priority host perf events (e.g. cpu pinned) could reclaim the\n * pmu resources (e.g. LBR) that were assigned to the guest. This is\ndiff --git a/arch/x86/kvm/vmx/pmu_intel.h b/arch/x86/kvm/vmx/pmu_intel.h\nindex 5d9357640aa18..b553f63e19a67 100644\n--- a/arch/x86/kvm/vmx/pmu_intel.h\n+++ b/arch/x86/kvm/vmx/pmu_intel.h\n@@ -34,7 +34,12 @@ struct lbr_desc {\n \t /\n \tstruct perf_event event;\n \n-\t/* True if LBRs are marked as not intercepted in the MSR bitmap /\n+\t/\n+\t * True if KVM wants the LBR MSRs to be passed through, i.e. not\n+\t * intercepted. Note, userspace MSR filters may force interception of\n+\t * some or all LBR MSRs regardless, i.e. this doesn't necessarily\n+\t * reflect the state of the MSR bitmap.\n+\t /\n \tbool msr_passthrough;\n };\n \ndiff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c\nindex 612ab07d4100f..1c190a6303a36 100644\n--- a/arch/x86/kvm/vmx/vmx.c\n+++ b/arch/x86/kvm/vmx/vmx.c\n@@ -4347,11 +4347,13 @@ static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu)\n \t\tvmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept);\n \t}\n \n+\tvmx_recalc_lbr_msr_intercepts(vcpu);\n+\n \tvmx_recalc_pmu_msr_intercepts(vcpu);\n \n \t/\n-\t x2APIC and LBR MSR intercepts are modified on-demand and cannot be\n-\t * filtered by userspace.\n+\t * x2APIC intercepts are modified on-demand and cannot be filtered by\n+\t * userspace.\n \t /\n }\n \ndiff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h\nindex dc8517f15bc46..ec6104b660090 100644\n--- a/arch/x86/kvm/vmx/vmx.h\n+++ b/arch/x86/kvm/vmx/vmx.h\n@@ -667,6 +667,7 @@ static __always_inline struct vcpu_vmx to_vmx(struct kvm_vcpu vcpu)\n void intel_pmu_cross_mapped_check(struct kvm_pmu pmu);\n int intel_pmu_create_guest_lbr_event(struct kvm_vcpu vcpu);\n void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu);\n+void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu);\n \n struct vmcs alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags);\n void free_vmcs(struct vmcs vmcs);\ndiff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm\nindex f43549a56f0b2..9cefaf64809da 100644\n--- a/tools/testing/selftests/kvm/Makefile.kvm\n+++ b/tools/testing/selftests/kvm/Makefile.kvm\n@@ -92,6 +92,7 @@ TEST_GEN_PROGS_x86 += x86/kvm_clock_test\n TEST_GEN_PROGS_x86 += x86/kvm_pv_test\n TEST_GEN_PROGS_x86 += x86/kvm_buslock_test\n TEST_GEN_PROGS_x86 += x86/monitor_mwait_test\n+TEST_GEN_PROGS_x86 += x86/msr_filter_update_test\n TEST_GEN_PROGS_x86 += x86/msrs_test\n TEST_GEN_PROGS_x86 += x86/nested_close_kvm_test\n TEST_GEN_PROGS_x86 += x86/nested_dirty_log_test\ndiff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h\nindex 6e6f70035508a..6e9db81187c34 100644\n--- a/tools/testing/selftests/kvm/include/x86/processor.h\n+++ b/tools/testing/selftests/kvm/include/x86/processor.h\n@@ -1530,8 +1530,12 @@ static inline void cli(void)\n \tasm volatile (\"cli\");\n }\n \n+bool __vm_xsave_request_permission(u64 xfeature, const char name);\n void __vm_xsave_require_permission(u64 xfeature, const char name);\n \n+#define vm_xsave_request_permission(xfeature)\t\\\n+\t__vm_xsave_request_permission(xfeature, #xfeature)\n+\n #define vm_xsave_require_permission(xfeature)\t\\\n \t__vm_xsave_require_permission(xfeature, #xfeature)\n \ndiff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c\nindex d31fa81ea0756..12092e59b3905 100644\n--- a/tools/testing/selftests/kvm/lib/x86/processor.c\n+++ b/tools/testing/selftests/kvm/lib/x86/processor.c\n@@ -975,16 +975,18 @@ u64 kvm_get_feature_msr(u64 msr_index)\n \treturn buffer.entry.data;\n }\n \n-void __vm_xsave_require_permission(u64 xfeature, const char name)\n+/\n+ Request permission for guests to use the dynamic XSAVE feature @xfeature.\n+ * Returns false, without skipping the test, if KVM doesn't support the\n+ * feature or if the request is denied. Must be called before\n+ * KVM_GET_SUPPORTED_CPUID is first queried, as KVM enumerates dynamic\n+ * features only if userspace has permission to use them.\n+ /\n+bool __vm_xsave_request_permission(u64 xfeature, const char name)\n {\n \tint kvm_fd;\n \tu64 bitmask;\n \tlong rc;\n-\tstruct kvm_device_attr attr = {\n-\t\t.group = 0,\n-\t\t.attr = KVM_X86_XCOMP_GUEST_SUPP,\n-\t\t.addr = (unsigned long) \u0026bitmask,\n-\t};\n \n \tTEST_ASSERT(!kvm_supported_cpuid,\n \t\t \"kvm_get_supported_cpuid() cannot be used before ARCH_REQ_XCOMP_GUEST_PERM\");\n@@ -993,24 +995,33 @@ void __vm_xsave_require_permission(u64 xfeature, const char name)\n \t\t \"Dynamic XFeatures must be enabled one at a time\");\n \n \tkvm_fd = open_kvm_dev_path_or_exit();\n-\trc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, \u0026attr);\n+\trc = __kvm_device_attr_get(kvm_fd, 0, KVM_X86_XCOMP_GUEST_SUPP, \u0026bitmask);\n \tclose(kvm_fd);\n \n \tif (rc == -1 \u0026\u0026 (errno == ENXIO \|\| errno == EINVAL))\n-\t\t__TEST_REQUIRE(0, \"KVM_X86_XCOMP_GUEST_SUPP not supported\");\n+\t\treturn false;\n \n \tTEST_ASSERT(rc == 0, \"KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld\", rc);\n \n-\t__TEST_REQUIRE(bitmask \u0026 xfeature,\n-\t\t \"Required XSAVE feature '%s' not supported\", name);\n+\tif (!(bitmask \u0026 xfeature))\n+\t\treturn false;\n \n-\tTEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature)));\n+\tif (syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature)))\n+\t\treturn false;\n \n \trc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, \u0026bitmask);\n \tTEST_ASSERT(rc == 0, \"prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld\", rc);\n \tTEST_ASSERT(bitmask \u0026 xfeature,\n \t\t \"'%s' (0x%lx) not permitted after prctl(ARCH_REQ_XCOMP_GUEST_PERM) permitted=0x%lx\",\n \t\t name, xfeature, bitmask);\n+\treturn true;\n+}\n+\n+void __vm_xsave_require_permission(u64 xfeature, const char name)\n+{\n+\t__TEST_REQUIRE(__vm_xsave_request_permission(xfeature, name),\n+\t\t \"Dynamic XSAVE feature '%s' not supported or not permitted\",\n+\t\t name);\n }\n \n void vcpu_init_cpuid(struct kvm_vcpu vcpu, const struct kvm_cpuid2 cpuid)\ndiff --git a/tools/testing/selftests/kvm/x86/msr_filter_update_test.c b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c\nnew file mode 100644\nindex 0000000000000..9b9ba3fa398c8\n--- /dev/null\n+++ b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c\n@@ -0,0 +1,392 @@\n+// SPDX-License-Identifier: GPL-2.0-only\n+/\n+ Copyright (C) 2026, Google LLC.\n+ \n+ Verify that changes to userspace MSR filters take effect for MSRs that KVM\n+ * has already passed through to the guest, i.e. that KVM refreshes its MSR\n+ * bitmaps on filter changes even if its desired interception hasn't changed.\n+ \n+ Intel PT MSRs aren't covered, as KVM passes them through only while the\n+ * guest is tracing (RTIT_CTL.TraceEn=1), which requires valid output setup.\n+ /\n+#include \"kvm_util.h\"\n+#include \"processor.h\"\n+\n+#define ACC_R\tKVM_MSR_FILTER_READ\n+#define ACC_W\tKVM_MSR_FILTER_WRITE\n+#define ACC_RW\t(ACC_R \| ACC_W)\n+\n+struct test_msr {\n+\tu32 index;\n+\tconst char name;\n+\t/* Accesses to perform; never write MSRs where doing so is unsafe. /\n+\tu8 access;\n+\t/ Value to write for write-only MSRs. /\n+\tu64 write_val;\n+};\n+\n+/ Stringify in the outer macros, before the MSR name is macro-expanded. /\n+#define __MSR(msr, str, acc, val)\t\t\t\t\t\\\n+\t{ .index = msr, .name = str, .access = acc, .write_val = val }\n+#define MSR_R(msr)\t\t__MSR(msr, #msr, ACC_R, 0)\n+#define MSR_W(msr, val)\t\t__MSR(msr, #msr, ACC_W, val)\n+#define MSR_RW(msr)\t\t__MSR(msr, #msr, ACC_RW, 0)\n+\n+/\n+ * MSRs that KVM may pass through to the guest on Intel and/or AMD. MSRs that\n+ * don't exist on the host, or that KVM doesn't support for the guest, are\n+ * still useful: denied accesses must exit to userspace regardless of whether\n+ * KVM would have emulated or rejected them.\n+ /\n+static const struct test_msr msrs[] = {\n+\tMSR_R(MSR_IA32_TSC),\n+\tMSR_RW(MSR_IA32_SPEC_CTRL),\n+\tMSR_W(MSR_IA32_PRED_CMD, PRED_CMD_IBPB),\n+\tMSR_W(MSR_IA32_FLUSH_CMD, L1D_FLUSH),\n+\tMSR_RW(MSR_IA32_SYSENTER_CS),\n+\tMSR_RW(MSR_IA32_SYSENTER_ESP),\n+\tMSR_RW(MSR_IA32_SYSENTER_EIP),\n+\tMSR_R(MSR_IA32_APERF),\n+\tMSR_R(MSR_IA32_MPERF),\n+\tMSR_R(MSR_CORE_C1_RES),\n+\tMSR_R(MSR_CORE_C3_RESIDENCY),\n+\tMSR_R(MSR_CORE_C6_RESIDENCY),\n+\tMSR_R(MSR_CORE_C7_RESIDENCY),\n+\tMSR_RW(MSR_IA32_XFD),\n+\tMSR_RW(MSR_IA32_XFD_ERR),\n+\n+\t/ LBRs: AMD LBR virtualization, and Intel's legacy LBR stack. /\n+\tMSR_RW(MSR_IA32_DEBUGCTLMSR),\n+\tMSR_RW(MSR_IA32_LASTBRANCHFROMIP),\n+\tMSR_RW(MSR_IA32_LASTBRANCHTOIP),\n+\tMSR_RW(MSR_IA32_LASTINTFROMIP),\n+\tMSR_RW(MSR_IA32_LASTINTTOIP),\n+\tMSR_RW(MSR_LBR_SELECT),\n+\tMSR_RW(MSR_LBR_TOS),\n+\tMSR_RW(MSR_LBR_CORE_FROM),\n+\tMSR_RW(MSR_LBR_CORE_TO),\n+\tMSR_RW(MSR_LBR_NHM_FROM),\n+\tMSR_RW(MSR_LBR_NHM_TO),\n+\tMSR_RW(MSR_LBR_INFO_0),\n+\n+\t/ CET. /\n+\tMSR_RW(MSR_IA32_U_CET),\n+\tMSR_RW(MSR_IA32_S_CET),\n+\tMSR_RW(MSR_IA32_PL0_SSP),\n+\tMSR_RW(MSR_IA32_PL1_SSP),\n+\tMSR_RW(MSR_IA32_PL2_SSP),\n+\tMSR_RW(MSR_IA32_PL3_SSP),\n+\n+\t/ Mediated PMU, Intel. /\n+\tMSR_RW(MSR_IA32_PERFCTR0),\n+\tMSR_RW(MSR_IA32_PMC0),\n+\tMSR_RW(MSR_CORE_PERF_FIXED_CTR0),\n+\tMSR_R(MSR_CORE_PERF_GLOBAL_STATUS),\n+\tMSR_RW(MSR_CORE_PERF_GLOBAL_CTRL),\n+\tMSR_W(MSR_CORE_PERF_GLOBAL_OVF_CTRL, 0),\n+\n+\t/ Mediated PMU, AMD. /\n+\tMSR_RW(MSR_K7_PERFCTR0),\n+\tMSR_RW(MSR_F15H_PERF_CTR),\n+\tMSR_R(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS),\n+\tMSR_RW(MSR_AMD64_PERF_CNTR_GLOBAL_CTL),\n+\tMSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR, 0),\n+\tMSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_SET, 0),\n+\n+\tMSR_RW(MSR_STAR),\n+\tMSR_RW(MSR_LSTAR),\n+\tMSR_RW(MSR_CSTAR),\n+\tMSR_RW(MSR_SYSCALL_MASK),\n+\tMSR_RW(MSR_FS_BASE),\n+\tMSR_RW(MSR_GS_BASE),\n+\tMSR_RW(MSR_KERNEL_GS_BASE),\n+};\n+\n+#define NR_MSRS ARRAY_SIZE(msrs)\n+\n+/\n+ * Accesses denied by the filter in each phase. The sequence covers every\n+ * possible transition between the four filter states (allow all, deny reads,\n+ * deny writes, deny both), to catch KVM failing to propagate filter changes\n+ * from any prior state.\n+ /\n+static const u8 phases[] = {\n+\t0, ACC_RW, 0, ACC_R, 0, ACC_W, ACC_R, ACC_RW, ACC_W, ACC_RW, ACC_R,\n+\tACC_W, 0,\n+};\n+\n+/ MSR filter ranges, which must cover every MSR in msrs[]. /\n+static const u32 filter_bases[] = { 0x00000000, 0xc0000000, 0xc0010000 };\n+#define FILTER_NR_MSRS\t(KVM_MSR_FILTER_MAX_BITMAP_SIZE BITS_PER_BYTE)\n+\n+/* All zeroes, i.e. deny everything in the range. /\n+static u8 deny_bitmap[KVM_MSR_FILTER_MAX_BITMAP_SIZE];\n+\n+/ Guest-only: the last value read from each MSR with no filter in place. /\n+static u64 guest_vals[NR_MSRS];\n+static bool guest_val_valid[NR_MSRS];\n+\n+/ Host-only: userspace exits observed during the current phase. /\n+static int nr_read_exits[NR_MSRS];\n+static int nr_write_exits[NR_MSRS];\n+\n+/\n+ * Get KVM to pass through as many MSRs as possible. Failures are expected\n+ * and ignored, e.g. if the relevant feature isn't supported.\n+ /\n+static void guest_prime_passthrough(void)\n+{\n+\tstatic const u64 spec_ctrl_vals[] = {\n+\t\tSPEC_CTRL_IBRS, SPEC_CTRL_STIBP, SPEC_CTRL_SSBD,\n+\t};\n+\tint i;\n+\n+\t/\n+\t * Enabling LBRs activates LBR virtualization on AMD, and creates a\n+\t * guest LBR perf event (and thus passes through the LBR stack) on\n+\t * Intel.\n+\t /\n+\twrmsr_safe(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_LBR);\n+\n+\t/ KVM passes through SPEC_CTRL once the guest sets a non-zero value. /\n+\tfor (i = 0; i \u003c ARRAY_SIZE(spec_ctrl_vals); i++) {\n+\t\tif (!wrmsr_safe(MSR_IA32_SPEC_CTRL, spec_ctrl_vals[i]))\n+\t\t\tbreak;\n+\t}\n+\n+\t/ VMX passes through XFD once the guest sets a non-zero value. /\n+\twrmsr_safe(MSR_IA32_XFD, XFEATURE_MASK_XTILE_DATA);\n+}\n+\n+static void guest_access_msrs(u8 deny)\n+{\n+\tu64 val;\n+\tint i;\n+\n+\tfor (i = 0; i \u003c NR_MSRS; i++) {\n+\t\tconst struct test_msr msr = \u0026msrs[i];\n+\n+\t\t/\n+\t\t Denied reads are handled by userspace, so only record the\n+\t\t * value if the read is allowed (and doesn't #GP).\n+\t\t /\n+\t\tif (msr-\u003eaccess \u0026 ACC_R) {\n+\t\t\tif (!rdmsr_safe(msr-\u003eindex, \u0026val) \u0026\u0026 !(deny \u0026 ACC_R)) {\n+\t\t\t\tguest_vals[i] = val;\n+\t\t\t\tguest_val_valid[i] = true;\n+\t\t\t}\n+\t\t}\n+\n+\t\tif (!(msr-\u003eaccess \u0026 ACC_W))\n+\t\t\tcontinue;\n+\n+\t\tif (!(msr-\u003eaccess \u0026 ACC_R))\n+\t\t\tval = msr-\u003ewrite_val;\n+\t\telse if (guest_val_valid[i])\n+\t\t\tval = guest_vals[i];\n+\t\telse if (deny \u0026 ACC_W)\n+\t\t\tval = 0;\n+\t\telse\n+\t\t\tcontinue;\n+\n+\t\t/\n+\t\t * Writes that are allowed only ever write the MSR's current\n+\t\t * (or a benign) value. Denied writes are dropped by userspace.\n+\t\t /\n+\t\twrmsr_safe(msr-\u003eindex, val);\n+\t}\n+}\n+\n+static void guest_code(void)\n+{\n+\tint i;\n+\n+\tguest_prime_passthrough();\n+\n+\tfor (i = 0; i \u003c ARRAY_SIZE(phases); i++) {\n+\t\tguest_access_msrs(phases[i]);\n+\t\tGUEST_SYNC(i);\n+\t}\n+\n+\tGUEST_DONE();\n+}\n+\n+static void set_msr_filter(struct kvm_vm vm, u8 deny)\n+{\n+\tstruct kvm_msr_filter filter = {\n+\t\t.flags = KVM_MSR_FILTER_DEFAULT_ALLOW,\n+\t};\n+\tint i;\n+\n+\t/* No ranges, i.e. disable filtering, if nothing is denied. /\n+\tif (deny) {\n+\t\tfor (i = 0; i \u003c ARRAY_SIZE(filter_bases); i++) {\n+\t\t\tfilter.ranges[i].flags = deny;\n+\t\t\tfilter.ranges[i].base = filter_bases[i];\n+\t\t\tfilter.ranges[i].nmsrs = FILTER_NR_MSRS;\n+\t\t\tfilter.ranges[i].bitmap = deny_bitmap;\n+\t\t}\n+\t}\n+\n+\tvm_ioctl(vm, KVM_X86_SET_MSR_FILTER, \u0026filter);\n+}\n+\n+static int find_msr(u32 index)\n+{\n+\tint i;\n+\n+\tfor (i = 0; i \u003c NR_MSRS; i++) {\n+\t\tif (msrs[i].index == index)\n+\t\t\treturn i;\n+\t}\n+\n+\tTEST_FAIL(\"Unexpected userspace exit for MSR 0x%x\", index);\n+\treturn -1;\n+}\n+\n+static void handle_msr_exit(struct kvm_vcpu vcpu)\n+{\n+\tstruct kvm_run run = vcpu-\u003erun;\n+\tint i = find_msr(run-\u003emsr.index);\n+\n+\tTEST_ASSERT(run-\u003emsr.reason == KVM_MSR_EXIT_REASON_FILTER,\n+\t\t \"Wanted KVM_MSR_EXIT_REASON_FILTER for %s, got reason %u\",\n+\t\t msrs[i].name, run-\u003emsr.reason);\n+\n+\tif (run-\u003eexit_reason == KVM_EXIT_X86_RDMSR) {\n+\t\tnr_read_exits[i]++;\n+\t\trun-\u003emsr.data = 0;\n+\t} else {\n+\t\tnr_write_exits[i]++;\n+\t}\n+\trun-\u003emsr.error = 0;\n+}\n+\n+static int check_exits(const char type, const char name, int nr_exits,\n+\t\t bool denied, int phase)\n+{\n+\tint expected = denied;\n+\n+\tif (nr_exits == expected)\n+\t\treturn 0;\n+\n+\tpr_info(\"Phase %d: %s %s: wanted %d userspace exit(s), got %d\\n\",\n+\t\tphase, name, type, expected, nr_exits);\n+\treturn 1;\n+}\n+\n+static void verify_phase(int phase)\n+{\n+\tu8 deny = phases[phase];\n+\tint i, nr_failures = 0;\n+\n+\tfor (i = 0; i \u003c NR_MSRS; i++) {\n+\t\tnr_failures += check_exits(\"RDMSR\", msrs[i].name,\n+\t\t\t\t\t nr_read_exits[i],\n+\t\t\t\t\t msrs[i].access \u0026 deny \u0026 ACC_R, phase);\n+\t\tnr_failures += check_exits(\"WRMSR\", msrs[i].name,\n+\t\t\t\t\t nr_write_exits[i],\n+\t\t\t\t\t msrs[i].access \u0026 deny \u0026 ACC_W, phase);\n+\t}\n+\n+\tTEST_ASSERT(!nr_failures,\n+\t\t \"Phase %d (deny =%s%s): %d MSR filter failure(s), see above\",\n+\t\t phase, deny \u0026 ACC_R ? \" RDMSR\" : \"\",\n+\t\t deny \u0026 ACC_W ? \" WRMSR\" : \"\", nr_failures);\n+}\n+\n+static void run_phase(struct kvm_vcpu vcpu, int phase)\n+{\n+\tstruct ucall uc;\n+\n+\tmemset(nr_read_exits, 0, sizeof(nr_read_exits));\n+\tmemset(nr_write_exits, 0, sizeof(nr_write_exits));\n+\n+\tset_msr_filter(vcpu-\u003evm, phases[phase]);\n+\n+\tfor (;;) {\n+\t\tvcpu_run(vcpu);\n+\n+\t\tif (vcpu-\u003erun-\u003eexit_reason == KVM_EXIT_X86_RDMSR \|\|\n+\t\t vcpu-\u003erun-\u003eexit_reason == KVM_EXIT_X86_WRMSR) {\n+\t\t\thandle_msr_exit(vcpu);\n+\t\t\tcontinue;\n+\t\t}\n+\n+\t\tTEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);\n+\n+\t\tswitch (get_ucall(vcpu, \u0026uc)) {\n+\t\tcase UCALL_SYNC:\n+\t\t\tTEST_ASSERT_EQ(uc.args[1], phase);\n+\t\t\tverify_phase(phase);\n+\t\t\treturn;\n+\t\tcase UCALL_ABORT:\n+\t\t\tREPORT_GUEST_ASSERT(uc);\n+\t\tdefault:\n+\t\t\tTEST_FAIL(\"Unexpected ucall %lu\", uc.cmd);\n+\t\t}\n+\t}\n+}\n+\n+int main(int argc, char argv[])\n+{\n+\tu64 disable_exits;\n+\tstruct kvm_vcpu vcpu;\n+\tstruct kvm_vm vm;\n+\tstruct ucall uc;\n+\tint i, j;\n+\n+\tTEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_USER_SPACE_MSR));\n+\tTEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_MSR_FILTER));\n+\n+\tfor (i = 0; i \u003c NR_MSRS; i++) {\n+\t\tfor (j = 0; j \u003c i; j++)\n+\t\t\tTEST_ASSERT(msrs[i].index != msrs[j].index,\n+\t\t\t\t \"%s (0x%x) is listed more than once\",\n+\t\t\t\t msrs[i].name, msrs[i].index);\n+\n+\t\tfor (j = 0; j \u003c ARRAY_SIZE(filter_bases); j++) {\n+\t\t\tif (msrs[i].index - filter_bases[j] \u003c FILTER_NR_MSRS)\n+\t\t\t\tbreak;\n+\t\t}\n+\t\tTEST_ASSERT(j \u003c ARRAY_SIZE(filter_bases),\n+\t\t\t \"%s (0x%x) isn't covered by the MSR filter\",\n+\t\t\t msrs[i].name, msrs[i].index);\n+\t}\n+\n+\t/\n+\t * Request permission to expose AMX to the guest, if possible, so that\n+\t * the guest can set XFD. Ignore failure, as KVM omits AMX (and thus\n+\t * support for non-zero XFD values) from the supported CPUID if\n+\t * permission isn't granted, and priming XFD is done on a best effort\n+\t * basis.\n+\t /\n+\tvm_xsave_request_permission(XFEATURE_MASK_XTILE_DATA);\n+\n+\tvm = vm_create(1);\n+\n+\t/\n+\t * Pass through APERF/MPERF and the C-state residency MSRs if allowed.\n+\t * This must be done before creating vCPUs.\n+\t /\n+\tdisable_exits = vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS) \u0026\n+\t\t\t(KVM_X86_DISABLE_EXITS_APERFMPERF \|\n+\t\t\t KVM_X86_DISABLE_EXITS_CSTATE);\n+\tif (disable_exits)\n+\t\tvm_enable_cap(vm, KVM_CAP_X86_DISABLE_EXITS, disable_exits);\n+\n+\t/ Userspace exits must be enabled before installing any filters. */\n+\tvm_enable_cap(vm, KVM_CAP_X86_USER_SPACE_MSR, KVM_MSR_EXIT_REASON_FILTER);\n+\n+\tvcpu = vm_vcpu_add(vm, 0, guest_code);\n+\n+\tfor (i = 0; i \u003c ARRAY_SIZE(phases); i++)\n+\t\trun_phase(vcpu, i);\n+\n+\tvcpu_run(vcpu);\n+\tTEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);\n+\tTEST_ASSERT_EQ(get_ucall(vcpu, \u0026uc), UCALL_DONE);\n+\n+\tkvm_vm_free(vm);\n+\treturn 0;\n+}\n" }
2/1	2026/10/21 08:12	agent	patch-evaluator	2m Model: core Args: null Results: { "EnableConfigs": [ "KVM", "KVM_INTEL", "KVM_AMD" ], "FocusSymbols": [ "vmx_recalc_lbr_msr_intercepts", "svm_set_lbr_msr_intercepts", "svm_recalc_lbr_msr_intercepts", "svm_update_lbrv", "kvm_vm_ioctl_set_msr_filter", "vmx_recalc_intercepts" ], "Reasoning": "The patch series updates KVM's MSR intercept recalculation logic for both Intel VMX and AMD SVM to ensure userspace MSR filter changes are reflected for passed-through LBR MSRs. It introduces vmx_recalc_lbr_msr_intercepts() with a new WARN_ON_ONCE assertion, refactors svm_recalc_lbr_msr_intercepts()/svm_set_lbr_msr_intercepts(), and hooks them into intercept recalculation paths triggered by KVM_X86_SET_MSR_FILTER. These changes touch reachable core virtualization code accessible via /dev/kvm ioctls and guest operations.", "WorthFuzzing": true } Instruction: You are an expert Linux kernel maintainer and security engineer. Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller. IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in your workspace. Do NOT rely on internal assumptions. You must actively use your code access tools to inspect the actual source code, callers, and surrounding context. ================================================================================ 1. CORE TRIAGE PHILOSOPHY ================================================================================ The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs, and newly triggered assertions introduced by the patch series. - REACHABILITY IS THE PRIMARY GATE: Fuzzing can only discover bugs in code that can actually execute in standard virtualized environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap). If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed, regardless of whether it adds assertions or complex logic. - DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS: Patch authors routinely label changes as "cleanups", "refactorings", or state "No functional change intended". Do NOT take these claims at face value. Code refactorings that rearrange logic, introduce helper functions, or alter state management in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs. If reachable executable code is modified or refactored, it MUST be fuzzed. - NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED: When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON, VM_WARN_ON, BUG_ON, lockdep_assert) in reachable code paths, it enforces new or stricter invariants. Even if the author believes the invariant always holds, fuzzing is essential to verify whether an unusual sequence of operations can violate it. ================================================================================ 2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA) ================================================================================ Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories: - Non-kernel and non-executable changes: * Modifications to Documentation/, comments, or spelling fixes. * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/) that do not affect the compiled kernel image (vmlinux) or kernel modules. * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints that do not alter control flow or data structures. * Build system or Kconfig changes that do not alter compiled C logic. - Structurally unreachable hardware: * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed, ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU. - Unreachable execution paths: * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during physical PCI hot-unplug or manual sysfs driver unbinding. * Code paths exclusive to architectures other than the target architecture. ================================================================================ 3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA) ================================================================================ Return WorthFuzzing=true whenever the patch touches reachable executable code, including: - Core Subsystems: * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/), BPF, scheduler, core networking, VFS, or syscall handling. - Refactorings and Code Cleanups: * Any restructuring of reachable data structures, helper abstractions, or algorithm flows. - Runtime Assertions and Defensive Checks: * Any introduction or alteration of assertions (WARN_ON, VM_WARN_ON, BUG_ON, etc.) in reachable paths. - Reachable Drivers and Protocols: Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.). ================================================================================ 4. EXTRACTING FocusSymbols (PREVENTING DILUTION) ================================================================================ When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer: - AVOID UBIQUITOUS LIFECYCLE HOT-PATHS: Do NOT list generic, ubiquitous functions called by almost every program in the corpus (including, but not limited to: general memory allocators and deallocators, page fault and trap handlers, or core synchronization primitives; this is not an exhaustive list). Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused", which severely dilutes fuzzing effort away from the actual changes. - TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS: List functions that specifically implement the logic being added or altered, or direct API entrypoints for the subsystem feature under review. - HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h): Compiler-inlined static functions (such as static inlines in mm/.h or include/linux/.h) lack distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters. If the changes are primarily in static inline helpers, identify non-static, feature-specific caller functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers). ================================================================================ 5. IDENTIFYING EnableConfigs ================================================================================ Identify any specific CONFIG_ options required to properly compile and reach the modified code: - Inspect Kconfig files and #ifdef guards; do not make assumptions. - Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed. - Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4"). Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 72ebad61c471673f43782933fb8f29af6aea0363 Author: syz-cluster <triage@syzkaller.com> Date: Wed Oct 21 08:12:40 2026 +0000 syz-cluster: applied patch under review diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index fe0cba4731b2e..55b3ee8403654 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -721,14 +721,11 @@ void svm_alloc_permissions_map(unsigned long size, gfp_t gfp_mask) return pm; } -static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +static void svm_set_lbr_msr_intercepts(struct kvm_vcpu vcpu) { struct vcpu_svm svm = to_svm(vcpu); bool intercept = !(svm->vmcb->control.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR); - if (intercept == svm->lbr_msrs_intercepted) - return; - svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHFROMIP, MSR_TYPE_RW, intercept); svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHTOIP, MSR_TYPE_RW, intercept); svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTINTFROMIP, MSR_TYPE_RW, intercept); @@ -740,6 +737,22 @@ static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) svm->lbr_msrs_intercepted = intercept; } +static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +{ + struct vcpu_svm svm = to_svm(vcpu); + bool intercept = !(svm->vmcb->control.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR); + + / + * Skip redundant updates from svm_update_lbrv(), e.g. on every nested + * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the + * bitmap unconditionally, as userspace MSR filters may have changed. + / + if (intercept == svm->lbr_msrs_intercepted) + return; + + svm_set_lbr_msr_intercepts(vcpu); +} + void svm_vcpu_free_msrpm(void msrpm) { __free_pages(virt_to_page(msrpm), get_order(MSRPM_SIZE)); @@ -795,8 +808,13 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu) svm_disable_intercept_for_msr(vcpu, MSR_SYSCALL_MASK, MSR_TYPE_RW); #endif + / + * Unconditionally refresh the LBR MSR intercepts, as userspace MSR + * filters may have changed, in which case the bitmap may be stale even + * if KVM's desired interception hasn't changed. + / if (lbrv) - svm_recalc_lbr_msr_intercepts(vcpu); + svm_set_lbr_msr_intercepts(vcpu); if (cpu_feature_enabled(X86_FEATURE_IBPB)) svm_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W, diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 84f19026d3e8b..62e08d6d4706e 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -364,6 +364,12 @@ struct vcpu_svm { bool avic_irq_window; bool x2avic_msrs_intercepted; + + / + * True if KVM wants the LBR MSRs to be intercepted. Note, userspace MSR + * filters may force interception regardless, i.e. this doesn't + * necessarily reflect the state of the MSR bitmap. + / bool lbr_msrs_intercepted; / Guest GIF value, used when vGIF is not enabled / diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c index 70a8c48161356..b945213f0b686 100644 --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -517,7 +517,8 @@ static void intel_pmu_refresh(struct kvm_vcpu vcpu) memset(&lbr_desc->records, 0, sizeof(lbr_desc->records)); /* - * Setting passthrough of LBR MSRs is done only in the VM-Entry loop, + * LBR MSRs are initially passed through only in the VM-Entry loop (a + * full MSR intercept recalc merely refreshes an existing passthrough), * and PMU refresh is disallowed after the vCPU has run, i.e. this code * should never be reached while KVM is passing through MSRs. / @@ -704,6 +705,23 @@ static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu) lbr_desc->msr_passthrough = true; } +/* + * Refresh the LBR MSR intercepts if the LBRs are passed through, so that + * changes to userspace MSR filters are reflected in the MSR bitmap. There's + * nothing to do if the LBRs are intercepted, as a filter can only force + * interception, never prevent it. + / +void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +{ + struct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu); + + if (WARN_ON_ONCE(!lbr_desc)) + return; + + if (lbr_desc->msr_passthrough) + vmx_update_intercept_for_lbr_msrs(vcpu, false); +} + / * Higher priority host perf events (e.g. cpu pinned) could reclaim the * pmu resources (e.g. LBR) that were assigned to the guest. This is diff --git a/arch/x86/kvm/vmx/pmu_intel.h b/arch/x86/kvm/vmx/pmu_intel.h index 5d9357640aa18..b553f63e19a67 100644 --- a/arch/x86/kvm/vmx/pmu_intel.h +++ b/arch/x86/kvm/vmx/pmu_intel.h @@ -34,7 +34,12 @@ struct lbr_desc { / struct perf_event event; - /* True if LBRs are marked as not intercepted in the MSR bitmap / + / + * True if KVM wants the LBR MSRs to be passed through, i.e. not + * intercepted. Note, userspace MSR filters may force interception of + * some or all LBR MSRs regardless, i.e. this doesn't necessarily + * reflect the state of the MSR bitmap. + / bool msr_passthrough; }; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 612ab07d4100f..1c190a6303a36 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -4347,11 +4347,13 @@ static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu) vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept); } + vmx_recalc_lbr_msr_intercepts(vcpu); + vmx_recalc_pmu_msr_intercepts(vcpu); /* - * x2APIC and LBR MSR intercepts are modified on-demand and cannot be - * filtered by userspace. + * x2APIC intercepts are modified on-demand and cannot be filtered by + * userspace. / } diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index dc8517f15bc46..ec6104b660090 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -667,6 +667,7 @@ static __always_inline struct vcpu_vmx to_vmx(struct kvm_vcpu vcpu) void intel_pmu_cross_mapped_check(struct kvm_pmu pmu); int intel_pmu_create_guest_lbr_event(struct kvm_vcpu vcpu); void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu); +void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu); struct vmcs alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags); void free_vmcs(struct vmcs vmcs); diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index f43549a56f0b2..9cefaf64809da 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -92,6 +92,7 @@ TEST_GEN_PROGS_x86 += x86/kvm_clock_test TEST_GEN_PROGS_x86 += x86/kvm_pv_test TEST_GEN_PROGS_x86 += x86/kvm_buslock_test TEST_GEN_PROGS_x86 += x86/monitor_mwait_test +TEST_GEN_PROGS_x86 += x86/msr_filter_update_test TEST_GEN_PROGS_x86 += x86/msrs_test TEST_GEN_PROGS_x86 += x86/nested_close_kvm_test TEST_GEN_PROGS_x86 += x86/nested_dirty_log_test diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h index 6e6f70035508a..6e9db81187c34 100644 --- a/tools/testing/selftests/kvm/include/x86/processor.h +++ b/tools/testing/selftests/kvm/include/x86/processor.h @@ -1530,8 +1530,12 @@ static inline void cli(void) asm volatile ("cli"); } +bool __vm_xsave_request_permission(u64 xfeature, const char name); void __vm_xsave_require_permission(u64 xfeature, const char name); +#define vm_xsave_request_permission(xfeature) \ + __vm_xsave_request_permission(xfeature, #xfeature) + #define vm_xsave_require_permission(xfeature) \ __vm_xsave_require_permission(xfeature, #xfeature) diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c index d31fa81ea0756..12092e59b3905 100644 --- a/tools/testing/selftests/kvm/lib/x86/processor.c +++ b/tools/testing/selftests/kvm/lib/x86/processor.c @@ -975,16 +975,18 @@ u64 kvm_get_feature_msr(u64 msr_index) return buffer.entry.data; } -void __vm_xsave_require_permission(u64 xfeature, const char name) +/* + * Request permission for guests to use the dynamic XSAVE feature @xfeature. + * Returns false, without skipping the test, if KVM doesn't support the + * feature or if the request is denied. Must be called before + * KVM_GET_SUPPORTED_CPUID is first queried, as KVM enumerates dynamic + * features only if userspace has permission to use them. + / +bool __vm_xsave_request_permission(u64 xfeature, const char name) { int kvm_fd; u64 bitmask; long rc; - struct kvm_device_attr attr = { - .group = 0, - .attr = KVM_X86_XCOMP_GUEST_SUPP, - .addr = (unsigned long) &bitmask, - }; TEST_ASSERT(!kvm_supported_cpuid, "kvm_get_supported_cpuid() cannot be used before ARCH_REQ_XCOMP_GUEST_PERM"); @@ -993,24 +995,33 @@ void __vm_xsave_require_permission(u64 xfeature, const char name) "Dynamic XFeatures must be enabled one at a time"); kvm_fd = open_kvm_dev_path_or_exit(); - rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr); + rc = __kvm_device_attr_get(kvm_fd, 0, KVM_X86_XCOMP_GUEST_SUPP, &bitmask); close(kvm_fd); if (rc == -1 && (errno == ENXIO \|\| errno == EINVAL)) - __TEST_REQUIRE(0, "KVM_X86_XCOMP_GUEST_SUPP not supported"); + return false; TEST_ASSERT(rc == 0, "KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld", rc); - __TEST_REQUIRE(bitmask & xfeature, - "Required XSAVE feature '%s' not supported", name); + if (!(bitmask & xfeature)) + return false; - TEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature))); + if (syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature))) + return false; rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask); TEST_ASSERT(rc == 0, "prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc); TEST_ASSERT(bitmask & xfeature, "'%s' (0x%lx) not permitted after prctl(ARCH_REQ_XCOMP_GUEST_PERM) permitted=0x%lx", name, xfeature, bitmask); + return true; +} + +void __vm_xsave_require_permission(u64 xfeature, const char name) +{ + __TEST_REQUIRE(__vm_xsave_request_permission(xfeature, name), + "Dynamic XSAVE feature '%s' not supported or not permitted", + name); } void vcpu_init_cpuid(struct kvm_vcpu vcpu, const struct kvm_cpuid2 cpuid) diff --git a/tools/testing/selftests/kvm/x86/msr_filter_update_test.c b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c new file mode 100644 index 0000000000000..9b9ba3fa398c8 --- /dev/null +++ b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c @@ -0,0 +1,392 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2026, Google LLC. + * + * Verify that changes to userspace MSR filters take effect for MSRs that KVM + * has already passed through to the guest, i.e. that KVM refreshes its MSR + * bitmaps on filter changes even if its desired interception hasn't changed. + * + * Intel PT MSRs aren't covered, as KVM passes them through only while the + * guest is tracing (RTIT_CTL.TraceEn=1), which requires valid output setup. + / +#include "kvm_util.h" +#include "processor.h" + +#define ACC_R KVM_MSR_FILTER_READ +#define ACC_W KVM_MSR_FILTER_WRITE +#define ACC_RW (ACC_R \| ACC_W) + +struct test_msr { + u32 index; + const char name; + /* Accesses to perform; never write MSRs where doing so is unsafe. / + u8 access; + / Value to write for write-only MSRs. / + u64 write_val; +}; + +/ Stringify in the outer macros, before the MSR name is macro-expanded. / +#define __MSR(msr, str, acc, val) \ + { .index = msr, .name = str, .access = acc, .write_val = val } +#define MSR_R(msr) __MSR(msr, #msr, ACC_R, 0) +#define MSR_W(msr, val) __MSR(msr, #msr, ACC_W, val) +#define MSR_RW(msr) __MSR(msr, #msr, ACC_RW, 0) + +/ + * MSRs that KVM may pass through to the guest on Intel and/or AMD. MSRs that + * don't exist on the host, or that KVM doesn't support for the guest, are + * still useful: denied accesses must exit to userspace regardless of whether + * KVM would have emulated or rejected them. + / +static const struct test_msr msrs[] = { + MSR_R(MSR_IA32_TSC), + MSR_RW(MSR_IA32_SPEC_CTRL), + MSR_W(MSR_IA32_PRED_CMD, PRED_CMD_IBPB), + MSR_W(MSR_IA32_FLUSH_CMD, L1D_FLUSH), + MSR_RW(MSR_IA32_SYSENTER_CS), + MSR_RW(MSR_IA32_SYSENTER_ESP), + MSR_RW(MSR_IA32_SYSENTER_EIP), + MSR_R(MSR_IA32_APERF), + MSR_R(MSR_IA32_MPERF), + MSR_R(MSR_CORE_C1_RES), + MSR_R(MSR_CORE_C3_RESIDENCY), + MSR_R(MSR_CORE_C6_RESIDENCY), + MSR_R(MSR_CORE_C7_RESIDENCY), + MSR_RW(MSR_IA32_XFD), + MSR_RW(MSR_IA32_XFD_ERR), + + / LBRs: AMD LBR virtualization, and Intel's legacy LBR stack. / + MSR_RW(MSR_IA32_DEBUGCTLMSR), + MSR_RW(MSR_IA32_LASTBRANCHFROMIP), + MSR_RW(MSR_IA32_LASTBRANCHTOIP), + MSR_RW(MSR_IA32_LASTINTFROMIP), + MSR_RW(MSR_IA32_LASTINTTOIP), + MSR_RW(MSR_LBR_SELECT), + MSR_RW(MSR_LBR_TOS), + MSR_RW(MSR_LBR_CORE_FROM), + MSR_RW(MSR_LBR_CORE_TO), + MSR_RW(MSR_LBR_NHM_FROM), + MSR_RW(MSR_LBR_NHM_TO), + MSR_RW(MSR_LBR_INFO_0), + + / CET. / + MSR_RW(MSR_IA32_U_CET), + MSR_RW(MSR_IA32_S_CET), + MSR_RW(MSR_IA32_PL0_SSP), + MSR_RW(MSR_IA32_PL1_SSP), + MSR_RW(MSR_IA32_PL2_SSP), + MSR_RW(MSR_IA32_PL3_SSP), + + / Mediated PMU, Intel. / + MSR_RW(MSR_IA32_PERFCTR0), + MSR_RW(MSR_IA32_PMC0), + MSR_RW(MSR_CORE_PERF_FIXED_CTR0), + MSR_R(MSR_CORE_PERF_GLOBAL_STATUS), + MSR_RW(MSR_CORE_PERF_GLOBAL_CTRL), + MSR_W(MSR_CORE_PERF_GLOBAL_OVF_CTRL, 0), + + / Mediated PMU, AMD. / + MSR_RW(MSR_K7_PERFCTR0), + MSR_RW(MSR_F15H_PERF_CTR), + MSR_R(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS), + MSR_RW(MSR_AMD64_PERF_CNTR_GLOBAL_CTL), + MSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR, 0), + MSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_SET, 0), + + MSR_RW(MSR_STAR), + MSR_RW(MSR_LSTAR), + MSR_RW(MSR_CSTAR), + MSR_RW(MSR_SYSCALL_MASK), + MSR_RW(MSR_FS_BASE), + MSR_RW(MSR_GS_BASE), + MSR_RW(MSR_KERNEL_GS_BASE), +}; + +#define NR_MSRS ARRAY_SIZE(msrs) + +/ + * Accesses denied by the filter in each phase. The sequence covers every + * possible transition between the four filter states (allow all, deny reads, + * deny writes, deny both), to catch KVM failing to propagate filter changes + * from any prior state. + / +static const u8 phases[] = { + 0, ACC_RW, 0, ACC_R, 0, ACC_W, ACC_R, ACC_RW, ACC_W, ACC_RW, ACC_R, + ACC_W, 0, +}; + +/ MSR filter ranges, which must cover every MSR in msrs[]. / +static const u32 filter_bases[] = { 0x00000000, 0xc0000000, 0xc0010000 }; +#define FILTER_NR_MSRS (KVM_MSR_FILTER_MAX_BITMAP_SIZE BITS_PER_BYTE) + +/* All zeroes, i.e. deny everything in the range. / +static u8 deny_bitmap[KVM_MSR_FILTER_MAX_BITMAP_SIZE]; + +/ Guest-only: the last value read from each MSR with no filter in place. / +static u64 guest_vals[NR_MSRS]; +static bool guest_val_valid[NR_MSRS]; + +/ Host-only: userspace exits observed during the current phase. / +static int nr_read_exits[NR_MSRS]; +static int nr_write_exits[NR_MSRS]; + +/ + * Get KVM to pass through as many MSRs as possible. Failures are expected + * and ignored, e.g. if the relevant feature isn't supported. + / +static void guest_prime_passthrough(void) +{ + static const u64 spec_ctrl_vals[] = { + SPEC_CTRL_IBRS, SPEC_CTRL_STIBP, SPEC_CTRL_SSBD, + }; + int i; + + / + * Enabling LBRs activates LBR virtualization on AMD, and creates a + * guest LBR perf event (and thus passes through the LBR stack) on + * Intel. + / + wrmsr_safe(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_LBR); + + / KVM passes through SPEC_CTRL once the guest sets a non-zero value. / + for (i = 0; i < ARRAY_SIZE(spec_ctrl_vals); i++) { + if (!wrmsr_safe(MSR_IA32_SPEC_CTRL, spec_ctrl_vals[i])) + break; + } + + / VMX passes through XFD once the guest sets a non-zero value. / + wrmsr_safe(MSR_IA32_XFD, XFEATURE_MASK_XTILE_DATA); +} + +static void guest_access_msrs(u8 deny) +{ + u64 val; + int i; + + for (i = 0; i < NR_MSRS; i++) { + const struct test_msr msr = &msrs[i]; + + /* + * Denied reads are handled by userspace, so only record the + * value if the read is allowed (and doesn't #GP). + / + if (msr->access & ACC_R) { + if (!rdmsr_safe(msr->index, &val) && !(deny & ACC_R)) { + guest_vals[i] = val; + guest_val_valid[i] = true; + } + } + + if (!(msr->access & ACC_W)) + continue; + + if (!(msr->access & ACC_R)) + val = msr->write_val; + else if (guest_val_valid[i]) + val = guest_vals[i]; + else if (deny & ACC_W) + val = 0; + else + continue; + + / + * Writes that are allowed only ever write the MSR's current + * (or a benign) value. Denied writes are dropped by userspace. + / + wrmsr_safe(msr->index, val); + } +} + +static void guest_code(void) +{ + int i; + + guest_prime_passthrough(); + + for (i = 0; i < ARRAY_SIZE(phases); i++) { + guest_access_msrs(phases[i]); + GUEST_SYNC(i); + } + + GUEST_DONE(); +} + +static void set_msr_filter(struct kvm_vm vm, u8 deny) +{ + struct kvm_msr_filter filter = { + .flags = KVM_MSR_FILTER_DEFAULT_ALLOW, + }; + int i; + + /* No ranges, i.e. disable filtering, if nothing is denied. / + if (deny) { + for (i = 0; i < ARRAY_SIZE(filter_bases); i++) { + filter.ranges[i].flags = deny; + filter.ranges[i].base = filter_bases[i]; + filter.ranges[i].nmsrs = FILTER_NR_MSRS; + filter.ranges[i].bitmap = deny_bitmap; + } + } + + vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter); +} + +static int find_msr(u32 index) +{ + int i; + + for (i = 0; i < NR_MSRS; i++) { + if (msrs[i].index == index) + return i; + } + + TEST_FAIL("Unexpected userspace exit for MSR 0x%x", index); + return -1; +} + +static void handle_msr_exit(struct kvm_vcpu vcpu) +{ + struct kvm_run run = vcpu->run; + int i = find_msr(run->msr.index); + + TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_FILTER, + "Wanted KVM_MSR_EXIT_REASON_FILTER for %s, got reason %u", + msrs[i].name, run->msr.reason); + + if (run->exit_reason == KVM_EXIT_X86_RDMSR) { + nr_read_exits[i]++; + run->msr.data = 0; + } else { + nr_write_exits[i]++; + } + run->msr.error = 0; +} + +static int check_exits(const char type, const char name, int nr_exits, + bool denied, int phase) +{ + int expected = denied; + + if (nr_exits == expected) + return 0; + + pr_info("Phase %d: %s %s: wanted %d userspace exit(s), got %d\n", + phase, name, type, expected, nr_exits); + return 1; +} + +static void verify_phase(int phase) +{ + u8 deny = phases[phase]; + int i, nr_failures = 0; + + for (i = 0; i < NR_MSRS; i++) { + nr_failures += check_exits("RDMSR", msrs[i].name, + nr_read_exits[i], + msrs[i].access & deny & ACC_R, phase); + nr_failures += check_exits("WRMSR", msrs[i].name, + nr_write_exits[i], + msrs[i].access & deny & ACC_W, phase); + } + + TEST_ASSERT(!nr_failures, + "Phase %d (deny =%s%s): %d MSR filter failure(s), see above", + phase, deny & ACC_R ? " RDMSR" : "", + deny & ACC_W ? " WRMSR" : "", nr_failures); +} + +static void run_phase(struct kvm_vcpu vcpu, int phase) +{ + struct ucall uc; + + memset(nr_read_exits, 0, sizeof(nr_read_exits)); + memset(nr_write_exits, 0, sizeof(nr_write_exits)); + + set_msr_filter(vcpu->vm, phases[phase]); + + for (;;) { + vcpu_run(vcpu); + + if (vcpu->run->exit_reason == KVM_EXIT_X86_RDMSR \|\| + vcpu->run->exit_reason == KVM_EXIT_X86_WRMSR) { + handle_msr_exit(vcpu); + continue; + } + + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); + + switch (get_ucall(vcpu, &uc)) { + case UCALL_SYNC: + TEST_ASSERT_EQ(uc.args[1], phase); + verify_phase(phase); + return; + case UCALL_ABORT: + REPORT_GUEST_ASSERT(uc); + default: + TEST_FAIL("Unexpected ucall %lu", uc.cmd); + } + } +} + +int main(int argc, char argv[]) +{ + u64 disable_exits; + struct kvm_vcpu vcpu; + struct kvm_vm vm; + struct ucall uc; + int i, j; + + TEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_USER_SPACE_MSR)); + TEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_MSR_FILTER)); + + for (i = 0; i < NR_MSRS; i++) { + for (j = 0; j < i; j++) + TEST_ASSERT(msrs[i].index != msrs[j].index, + "%s (0x%x) is listed more than once", + msrs[i].name, msrs[i].index); + + for (j = 0; j < ARRAY_SIZE(filter_bases); j++) { + if (msrs[i].index - filter_bases[j] < FILTER_NR_MSRS) + break; + } + TEST_ASSERT(j < ARRAY_SIZE(filter_bases), + "%s (0x%x) isn't covered by the MSR filter", + msrs[i].name, msrs[i].index); + } + + / + * Request permission to expose AMX to the guest, if possible, so that + * the guest can set XFD. Ignore failure, as KVM omits AMX (and thus + * support for non-zero XFD values) from the supported CPUID if + * permission isn't granted, and priming XFD is done on a best effort + * basis. + / + vm_xsave_request_permission(XFEATURE_MASK_XTILE_DATA); + + vm = vm_create(1); + + / + * Pass through APERF/MPERF and the C-state residency MSRs if allowed. + * This must be done before creating vCPUs. + / + disable_exits = vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS) & + (KVM_X86_DISABLE_EXITS_APERFMPERF \| + KVM_X86_DISABLE_EXITS_CSTATE); + if (disable_exits) + vm_enable_cap(vm, KVM_CAP_X86_DISABLE_EXITS, disable_exits); + + / Userspace exits must be enabled before installing any filters. */ + vm_enable_cap(vm, KVM_CAP_X86_USER_SPACE_MSR, KVM_MSR_EXIT_REASON_FILTER); + + vcpu = vm_vcpu_add(vm, 0, guest_code); + + for (i = 0; i < ARRAY_SIZE(phases); i++) + run_phase(vcpu, i); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); + TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_DONE); + + kvm_vm_free(vm); + return 0; +}
3/2	2026/10/21 08:12	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 12347 output: 37 thoughts: 1560 Thoughts: KVM Patch Analysis: Worth Fuzzing? Alright, let's break down this patch for KVM on amd64. First off, I see some restructuring related to LBR MSR intercepts in both the AMD (SVM) and Intel (VMX) virtualization modules. The key changes I'm noticing: * Refactoring in the SVM module: `svm_recalc_lbr_msr_intercepts` is split into `svm_set_lbr_msr_intercepts` and `svm_recalc_lbr_msr_intercepts`. Crucially, `svm_recalc_msr_intercepts` unconditionally calls `svm_set_lbr_msr_intercepts` when `lbrv` is set. * Similar changes in the VMX module: Introduction of `vmx_recalc_lbr_msr_intercepts`. The new function `vmx_recalc_lbr_msr_intercepts` in vmx includes a `WARN_ON_ONCE` which is very interesting. This points to a runtime check. And `vmx_recalc_msr_intercepts` calls `vmx_recalc_lbr_msr_intercepts`. * And there are self-test changes, but the core of the work is in the virtualization modules themselves. My initial question is: is this even fuzzable? Based on the guidelines, I need to determine if this code is reachable in a standard virtualized environment (QEMU/GCE). KVM is a core virtualization subsystem in `arch/x86/kvm/` and is accessed via `/dev/kvm` ioctls like `KVM_X86_SET_MSR_FILTER`, `KVM_RUN`, etc. So, the question becomes can I access KVM in QEMU? Yes! Nested virtualization is commonly enabled, or KVM is reachable if hardware virtualization is passed through (`-cpu host` in QEMU or nested virtualization in GCE). Syzkaller also has descriptions for `/dev/kvm`, so, yes, KVM is absolutely reachable. Looking at the guidelines, I see that the new `WARN_ON_ONCE` assertion, along with the logic changes, falls under positive criteria: runtime assertions, refactorings, and core subsystem changes, meaning this patch is very likely worth fuzzing. I need to now understand how the `svm_recalc_msr_intercepts` and `vmx_recalc_msr_intercepts` are called, which will need further investigation. I'll need to use `grepper` or manually read the code to track down the call sites.
4/2	2026/10/21 08:12	tool	grepper	0m Args: { "Expression": "recalc_msr_intercepts", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/sev.c=4718=int sev_es_string_io(struct vcpu_svm svm, int size, unsigned int port, int in)\n--\narch/x86/kvm/svm/sev.c-4741-\narch/x86/kvm/svm/sev.c:4742:void sev_es_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/sev.c-4743-{\n--\narch/x86/kvm/svm/svm.c=740=static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-746-\t Skip redundant updates from svm_update_lbrv(), e.g. on every nested\narch/x86/kvm/svm/svm.c:747:\t * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the\narch/x86/kvm/svm/svm.c-748-\t * bitmap unconditionally, as userspace MSR filters may have changed.\n--\narch/x86/kvm/svm/svm.c=761=static void svm_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-794-\narch/x86/kvm/svm/svm.c:795:static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-796-{\n--\narch/x86/kvm/svm/svm.c-865-\tif (is_sev_es_guest(vcpu))\narch/x86/kvm/svm/svm.c:866:\t\tsev_es_recalc_msr_intercepts(vcpu);\narch/x86/kvm/svm/svm.c-867-\n--\narch/x86/kvm/svm/svm.c=1129=static void svm_recalc_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-1131-\tsvm_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/svm/svm.c:1132:\tsvm_recalc_msr_intercepts(vcpu);\narch/x86/kvm/svm/svm.c-1133-}\n--\narch/x86/kvm/svm/svm.h=983=int sev_es_string_io(struct vcpu_svm svm, int size, unsigned int port, int in);\narch/x86/kvm/svm/svm.h:984:void sev_es_recalc_msr_intercepts(struct kvm_vcpu vcpu);\narch/x86/kvm/svm/svm.h-985-void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu vcpu, u8 vector);\n--\narch/x86/kvm/vmx/vmx.c=4228=static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4283-\narch/x86/kvm/vmx/vmx.c:4284:static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/vmx.c-4285-{\n--\narch/x86/kvm/vmx/vmx.c=4366=void vmx_recalc_intercepts(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4368-\tvmx_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c:4369:\tvmx_recalc_msr_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c-4370-}\n" }
5/2	2026/10/21 08:12	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 15653 output: 43 thoughts: 55 Thoughts: Okay, here's my take on those thought processes, tailored for an expert audience, and written in the first person: Analyzing MSR Interception Re-calculation Alright, I'm thinking we need to trace the call paths for those MSR intercept re-calculation functions, specifically `vmx_recalc_msr_intercepts`, `svm_recalc_msr_intercepts`, and the more general `vmx_recalc_intercepts` and `svm_recalc_intercepts`. I want to understand the conditions under which these are triggered. Are they tied to specific events like VM entry/exit, MSR access attempts, or perhaps certain control register modifications? Are there differences in their usage between VMX and SVM? Understanding this is critical for solidifying my grasp of the interception logic. Pinpointing the calling contexts will give me a better understanding of the overall behavior. I need to know why these recalculations are performed, when the intercepts need to be refreshed, and if there are any subtle differences based on the virtualization mode. This will help me identify potential optimization opportunities, security implications, or areas that might be prone to errors.
6/2	2026/10/21 08:13	tool	grepper	0m Args: { "Expression": "recalc_intercepts\|recalc_msr_intercepts", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/nested.c=127=static bool nested_vmcb_needs_vls_intercept(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-140-\narch/x86/kvm/svm/nested.c:141:void nested_vmcb02_recalc_intercepts(struct vcpu_svm svm)\narch/x86/kvm/svm/nested.c-142-{\n--\narch/x86/kvm/svm/nested.c=852=static void nested_vmcb02_prepare_control(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-1017-\t /\narch/x86/kvm/svm/nested.c:1018:\tnested_vmcb02_recalc_intercepts(svm);\narch/x86/kvm/svm/nested.c-1019-}\n--\narch/x86/kvm/svm/sev.c=4718=int sev_es_string_io(struct vcpu_svm svm, int size, unsigned int port, int in)\n--\narch/x86/kvm/svm/sev.c-4741-\narch/x86/kvm/svm/sev.c:4742:void sev_es_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/sev.c-4743-{\n--\narch/x86/kvm/svm/svm.c=740=static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-746-\t Skip redundant updates from svm_update_lbrv(), e.g. on every nested\narch/x86/kvm/svm/svm.c:747:\t * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the\narch/x86/kvm/svm/svm.c-748-\t * bitmap unconditionally, as userspace MSR filters may have changed.\n--\narch/x86/kvm/svm/svm.c=761=static void svm_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-794-\narch/x86/kvm/svm/svm.c:795:static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-796-{\n--\narch/x86/kvm/svm/svm.c-865-\tif (is_sev_es_guest(vcpu))\narch/x86/kvm/svm/svm.c:866:\t\tsev_es_recalc_msr_intercepts(vcpu);\narch/x86/kvm/svm/svm.c-867-\n--\narch/x86/kvm/svm/svm.c=1053=static void svm_recalc_instruction_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-1128-\narch/x86/kvm/svm/svm.c:1129:static void svm_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-1130-{\narch/x86/kvm/svm/svm.c-1131-\tsvm_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/svm/svm.c:1132:\tsvm_recalc_msr_intercepts(vcpu);\narch/x86/kvm/svm/svm.c-1133-}\n--\narch/x86/kvm/svm/svm.c=5343=struct kvm_x86_ops svm_x86_ops __initdata = {\n--\narch/x86/kvm/svm/svm.c-5478-\narch/x86/kvm/svm/svm.c:5479:\t.recalc_intercepts = svm_recalc_intercepts,\narch/x86/kvm/svm/svm.c-5480-\t.complete_emulated_msr = svm_complete_emulated_msr,\n--\narch/x86/kvm/svm/svm.h=549=static inline bool vmcb12_is_intercept(struct vmcb_ctrl_area_cached control, u32 bit)\n--\narch/x86/kvm/svm/svm.h-553-\narch/x86/kvm/svm/svm.h:554:void nested_vmcb02_recalc_intercepts(struct vcpu_svm svm);\narch/x86/kvm/svm/svm.h-555-\narch/x86/kvm/svm/svm.h=556=static inline void svm_mark_intercepts_dirty(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/svm.h-566-\tif (is_guest_mode(\u0026svm-\u003evcpu))\narch/x86/kvm/svm/svm.h:567:\t\tnested_vmcb02_recalc_intercepts(svm);\narch/x86/kvm/svm/svm.h-568-}\n--\narch/x86/kvm/svm/svm.h=983=int sev_es_string_io(struct vcpu_svm svm, int size, unsigned int port, int in);\narch/x86/kvm/svm/svm.h:984:void sev_es_recalc_msr_intercepts(struct kvm_vcpu vcpu);\narch/x86/kvm/svm/svm.h-985-void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu vcpu, u8 vector);\n--\narch/x86/kvm/vmx/main.c=196=static int vt_get_msr(struct kvm_vcpu vcpu, struct msr_data msr_info)\n--\narch/x86/kvm/vmx/main.c-203-\narch/x86/kvm/vmx/main.c:204:static void vt_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/main.c-205-{\n--\narch/x86/kvm/vmx/main.c-214-\narch/x86/kvm/vmx/main.c:215:\tvmx_recalc_intercepts(vcpu);\narch/x86/kvm/vmx/main.c-216-}\n--\narch/x86/kvm/vmx/main.c=888=struct kvm_x86_ops vt_x86_ops __initdata = {\n--\narch/x86/kvm/vmx/main.c-1027-\narch/x86/kvm/vmx/main.c:1028:\t.recalc_intercepts = vt_op(recalc_intercepts),\narch/x86/kvm/vmx/main.c-1029-\t.complete_emulated_msr = vt_op(complete_emulated_msr),\n--\narch/x86/kvm/vmx/vmx.c=4228=static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4283-\narch/x86/kvm/vmx/vmx.c:4284:static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/vmx.c-4285-{\n--\narch/x86/kvm/vmx/vmx.c=4360=static void vmx_recalc_instruction_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4365-\narch/x86/kvm/vmx/vmx.c:4366:void vmx_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/vmx.c-4367-{\narch/x86/kvm/vmx/vmx.c-4368-\tvmx_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c:4369:\tvmx_recalc_msr_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c-4370-}\n--\narch/x86/kvm/vmx/x86_ops.h=55=bool vmx_has_emulated_msr(struct kvm kvm, u32 index);\narch/x86/kvm/vmx/x86_ops.h:56:void vmx_recalc_intercepts(struct kvm_vcpu vcpu);\narch/x86/kvm/vmx/x86_ops.h-57-void vmx_prepare_switch_to_guest(struct kvm_vcpu vcpu);\n--\narch/x86/kvm/x86.c=8051=static int vcpu_enter_guest(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/x86.c-8211-\t\tif (kvm_check_request(KVM_REQ_RECALC_INTERCEPTS, vcpu))\narch/x86/kvm/x86.c:8212:\t\t\tkvm_x86_call(recalc_intercepts)(vcpu);\narch/x86/kvm/x86.c-8213-\n" }
7/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18620 output: 41 thoughts: 91 Thoughts: Here's my thought process, as if I were analyzing that code snippet: Diving into KVM Intercept Recalculation Okay, here's an interesting tidbit: the `kvm_check_request` function in `arch/x86/kvm/x86.c` seems to be responsible for handling a `KVM_REQ_RECALC_INTERCEPTS` request. My first thought is, where is this request set? I need to understand the trigger for this recalculation. This `kvm_x86_call` call to `recalc_intercepts` is probably the core logic, but I need the context. Let me trace back and see where `KVM_REQ_RECALC_INTERCEPTS` is actually being asserted. That's the key to understanding the control flow here. I'm going to follow the definition of that macro.
8/2	2026/10/21 08:13	tool	grepper	0m Args: { "Expression": "KVM_REQ_RECALC_INTERCEPTS", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/cpuid.c=376=void kvm_vcpu_after_set_cpuid(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/cpuid.c-468-\narch/x86/kvm/cpuid.c:469:\tkvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);\narch/x86/kvm/cpuid.c-470-}\n--\narch/x86/kvm/msrs.c=1442=int kvm_set_msr_common(struct kvm_vcpu vcpu, struct msr_data msr_info)\n--\narch/x86/kvm/msrs.c-1494-\t\tkvm_pmu_refresh(vcpu);\narch/x86/kvm/msrs.c:1495:\t\tkvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);\narch/x86/kvm/msrs.c-1496-\t\tbreak;\n--\narch/x86/kvm/msrs.c=2505=int kvm_vm_ioctl_set_msr_filter(struct kvm kvm, struct kvm_msr_filter filter)\n--\narch/x86/kvm/msrs.c-2546-\t /\narch/x86/kvm/msrs.c:2547:\tkvm_make_all_cpus_request(kvm, KVM_REQ_RECALC_INTERCEPTS);\narch/x86/kvm/msrs.c-2548-\n--\narch/x86/kvm/svm/svm.c=210=int svm_set_efer(struct kvm_vcpu vcpu, u64 efer)\n--\narch/x86/kvm/svm/svm.c-268-\t\tsvm_pmu_handle_nested_transition(svm);\narch/x86/kvm/svm/svm.c:269:\t\tkvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);\narch/x86/kvm/svm/svm.c-270-\t}\n--\narch/x86/kvm/svm/svm.c=1135=static void init_vmcb(struct kvm_vcpu vcpu, bool init_event)\n--\narch/x86/kvm/svm/svm.c-1283-\narch/x86/kvm/svm/svm.c:1284:\tkvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);\narch/x86/kvm/svm/svm.c-1285-\n--\narch/x86/kvm/x86.c=8051=static int vcpu_enter_guest(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/x86.c-8210-\narch/x86/kvm/x86.c:8211:\t\tif (kvm_check_request(KVM_REQ_RECALC_INTERCEPTS, vcpu))\narch/x86/kvm/x86.c-8212-\t\t\tkvm_x86_call(recalc_intercepts)(vcpu);\n" }
9/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19825 output: 32 thoughts: 1016 Thoughts: Analyzing MSR Intercept Recalculation in KVM Okay, so I need to dig into how MSR intercepts are recalculated within KVM, specifically focusing on the interactions that trigger these updates. I see that `kvm_vm_ioctl_set_msr_filter`, `kvm_vcpu_after_set_cpuid` (via `KVM_SET_CPUID` and `KVM_SET_CPUID2`), and `kvm_set_msr_common` (for MSR writes) all call `kvm_make_all_cpus_request(kvm, KVM_REQ_RECALC_INTERCEPTS)`. This is my starting point, as these are the obvious events that could impact MSR interception. Furthermore, `vcpu_enter_guest` processes the `KVM_REQ_RECALC_INTERCEPTS` request, which then calls `recalc_intercepts`. It's all connected. Now, let's drill down into the details of the changes. I'll start with the SVM code. In `arch/x86/kvm/svm/svm.c`, in `svm_recalc_msr_intercepts`, there's a new call to `svm_set_lbr_msr_intercepts` if LBR virtualization is enabled. Before, it was calling `svm_recalc_lbr_msr_intercepts`. I see that the original `svm_recalc_lbr_msr_intercepts` is now checking if an update is needed (redundant updates are skipped). The new function, `svm_set_lbr_msr_intercepts` actually does the MSR interception setting. I have to look at the details within the `svm_set_lbr_msr_intercepts` to fully understand what is changed and how these MSRs are being handled. Next I'll look at the VMX code. I find that `arch/x86/kvm/vmx/vmx.c` also calls `vmx_recalc_lbr_msr_intercepts` from `vmx_recalc_msr_intercepts`. Then in `arch/x86/kvm/vmx/pmu_intel.c`, the new function `vmx_update_intercept_for_lbr_msrs` is called if `lbr_desc->msr_passthrough` is set. Now I have the two main implementations of MSR intercept recalculation for LBR. Finally, I need to verify which Kconfig options are involved in enabling this functionality. The related KVM modules are `SVM` and `VMX`. I'll look for these in `arch/x86/kvm/Kconfig` to see the dependencies and configuration options.
10/2	2026/10/21 08:13	tool	grepper	0m Args: { "Expression": "config KVM", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/Kconfig=18=if VIRTUALIZATION\narch/x86/kvm/Kconfig-19-\narch/x86/kvm/Kconfig:20:config KVM_X86\narch/x86/kvm/Kconfig-21-\tdef_tristate KVM if (KVM_INTEL != n \|\| KVM_AMD != n)\n--\narch/x86/kvm/Kconfig-51-\narch/x86/kvm/Kconfig:52:config KVM\narch/x86/kvm/Kconfig-53-\ttristate \"Kernel-based Virtual Machine (KVM) support\"\n--\narch/x86/kvm/Kconfig-68-\narch/x86/kvm/Kconfig:69:config KVM_WERROR\narch/x86/kvm/Kconfig-70-\tbool \"Compile KVM with -Werror\"\n--\narch/x86/kvm/Kconfig-82-\narch/x86/kvm/Kconfig:83:config KVM_SW_PROTECTED_VM\narch/x86/kvm/Kconfig-84-\tbool \"Enable support for KVM software-protected VMs\"\n--\narch/x86/kvm/Kconfig-95-\narch/x86/kvm/Kconfig:96:config KVM_INTEL\narch/x86/kvm/Kconfig-97-\ttristate \"KVM for Intel (and compatible) processors support\"\n--\narch/x86/kvm/Kconfig-106-\narch/x86/kvm/Kconfig:107:config KVM_INTEL_PROVE_VE\narch/x86/kvm/Kconfig-108- bool \"Check that guests do not receive #VE exceptions\"\n--\narch/x86/kvm/Kconfig=122=config X86_SGX_KVM\n--\narch/x86/kvm/Kconfig-133-\narch/x86/kvm/Kconfig:134:config KVM_INTEL_TDX\narch/x86/kvm/Kconfig-135-\tbool \"Intel Trust Domain Extensions (TDX) support\"\n--\narch/x86/kvm/Kconfig-145-\narch/x86/kvm/Kconfig:146:config KVM_AMD\narch/x86/kvm/Kconfig-147-\ttristate \"KVM for AMD processors support\"\n--\narch/x86/kvm/Kconfig-155-\narch/x86/kvm/Kconfig:156:config KVM_AMD_SEV\narch/x86/kvm/Kconfig-157-\tbool \"AMD Secure Encrypted Virtualization (SEV) support\"\n--\narch/x86/kvm/Kconfig-172-\narch/x86/kvm/Kconfig:173:config KVM_IOAPIC\narch/x86/kvm/Kconfig-174-\tbool \"I/O APIC, PIC, and PIT emulation\"\n--\narch/x86/kvm/Kconfig-182-\narch/x86/kvm/Kconfig:183:config KVM_SMM\narch/x86/kvm/Kconfig-184-\tbool \"System Management Mode emulation\"\n--\narch/x86/kvm/Kconfig-193-\narch/x86/kvm/Kconfig:194:config KVM_HYPERV\narch/x86/kvm/Kconfig-195-\tbool \"Support for Microsoft Hyper-V emulation\"\n--\narch/x86/kvm/Kconfig-207-\narch/x86/kvm/Kconfig:208:config KVM_XEN\narch/x86/kvm/Kconfig-209-\tbool \"Support for Xen hypercall interface\"\n--\narch/x86/kvm/Kconfig-216-\narch/x86/kvm/Kconfig:217:config KVM_PROVE_MMU\narch/x86/kvm/Kconfig-218-\tbool \"Prove KVM MMU correctness\"\n--\narch/x86/kvm/Kconfig-229-\narch/x86/kvm/Kconfig:230:config KVM_EXTERNAL_WRITE_TRACKING\narch/x86/kvm/Kconfig-231-\tbool\narch/x86/kvm/Kconfig-232-\narch/x86/kvm/Kconfig:233:config KVM_MAX_NR_VCPUS\narch/x86/kvm/Kconfig-234-\tint \"Maximum number of vCPUs per KVM guest\"\n" }
11/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 22704 output: 39 thoughts: 30 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: Analyzing KVM Configuration Dependencies Alright, let's dive in. My immediate thought is to zero in on `arch/x86/kvm/Kconfig`. Specifically, I'm focusing on the section roughly between lines 50 and 150. That's usually the sweet spot for the core dependencies and feature flags for KVM on x86. I need to quickly get a mental map of what's tied to what. This area will expose all of the build time options, right? I need to understand what other kernel configurations are directly or indirectly impacting the KVM configuration. We're looking for dependencies here, right? Perhaps other architecture configs? Dependencies on other subsystems? Specific CPU features or model numbers? This is the starting point for tracing any potential conflicts or areas for optimization within the KVM build process. Time to grab a cup of coffee and get started.
12/2	2026/10/21 08:13	tool	read-file	0m Args: { "File": "arch/x86/kvm/Kconfig", "FirstLine": 50, "LineCount": 100 } Results: { "Contents": " 50:\t\tselect KVM_GUEST_MEMFD if X86_64\n 51:\t\n 52:\tconfig KVM\n 53:\t\ttristate \"Kernel-based Virtual Machine (KVM) support\"\n 54:\t\tdepends on X86_LOCAL_APIC\n 55:\t\thelp\n 56:\t\t Support hosting fully virtualized guest machines using hardware\n 57:\t\t virtualization extensions. You will need a fairly recent\n 58:\t\t processor equipped with virtualization extensions. You will also\n 59:\t\t need to select one or more of the processor modules below.\n 60:\t\n 61:\t\t This module provides access to the hardware capabilities through\n 62:\t\t a character device node named /dev/kvm.\n 63:\t\n 64:\t\t To compile this as a module, choose M here: the module\n 65:\t\t will be called kvm.\n 66:\t\n 67:\t\t If unsure, say N.\n 68:\t\n 69:\tconfig KVM_WERROR\n 70:\t\tbool \"Compile KVM with -Werror\"\n 71:\t\t# Disallow KVM's -Werror if KASAN is enabled, e.g. to guard against\n 72:\t\t# randomized configs from selecting KVM_WERROR=y, which doesn't play\n 73:\t\t# nice with KASAN. KASAN builds generates warnings for the default\n 74:\t\t# FRAME_WARN, i.e. KVM_WERROR=y with KASAN=y requires special tuning.\n 75:\t\t# Building KVM with -Werror and KASAN is still doable via enabling\n 76:\t\t# the kernel-wide WERROR=y.\n 77:\t\tdepends on KVM_X86 \u0026\u0026 ((EXPERT \u0026\u0026 !KASAN) \|\| WERROR)\n 78:\t\thelp\n 79:\t\t Add -Werror to the build flags for KVM.\n 80:\t\n 81:\t\t If in doubt, say \"N\".\n 82:\t\n 83:\tconfig KVM_SW_PROTECTED_VM\n 84:\t\tbool \"Enable support for KVM software-protected VMs\"\n 85:\t\tdepends on EXPERT\n 86:\t\tdepends on KVM_X86 \u0026\u0026 X86_64\n 87:\t\tselect KVM_GENERIC_MEMORY_ATTRIBUTES\n 88:\t\thelp\n 89:\t\t Enable support for KVM software-protected VMs. Currently, software-\n 90:\t\t protected VMs are purely a development and testing vehicle for\n 91:\t\t KVM_CREATE_GUEST_MEMFD. Attempting to run a \"real\" VM workload as a\n 92:\t\t software-protected VM will fail miserably.\n 93:\t\n 94:\t\t If unsure, say \"N\".\n 95:\t\n 96:\tconfig KVM_INTEL\n 97:\t\ttristate \"KVM for Intel (and compatible) processors support\"\n 98:\t\tdepends on KVM \u0026\u0026 IA32_FEAT_CTL\n 99:\t\tselect X86_FRED if X86_64\n 100:\t\thelp\n 101:\t\t Provides support for KVM on processors equipped with Intel's VT\n 102:\t\t extensions, a.k.a. Virtual Machine Extensions (VMX).\n 103:\t\n 104:\t\t To compile this as a module, choose M here: the module\n 105:\t\t will be called kvm-intel.\n 106:\t\n 107:\tconfig KVM_INTEL_PROVE_VE\n 108:\t bool \"Check that guests do not receive #VE exceptions\"\n 109:\t depends on KVM_INTEL \u0026\u0026 EXPERT\n 110:\t help\n 111:\t Checks that KVM's page table management code will not incorrectly\n 112:\t let guests receive a virtualization exception. Virtualization\n 113:\t exceptions will be trapped by the hypervisor rather than injected\n 114:\t in the guest.\n 115:\t\n 116:\t Note: some CPUs appear to generate spurious EPT Violations #VEs\n 117:\t that trigger KVM's WARN, in particular with eptad=0 and/or nested\n 118:\t virtualization.\n 119:\t\n 120:\t If unsure, say N.\n 121:\t\n 122:\tconfig X86_SGX_KVM\n 123:\t\tbool \"Software Guard eXtensions (SGX) Virtualization\"\n 124:\t\tdepends on X86_SGX \u0026\u0026 KVM_INTEL\n 125:\t\thelp\n 126:\t\n 127:\t\t Enables KVM guests to create SGX enclaves.\n 128:\t\n 129:\t\t This includes support to expose \"raw\" unreclaimable enclave memory to\n 130:\t\t guests via a device node, e.g. /dev/sgx_vepc.\n 131:\t\n 132:\t\t If unsure, say N.\n 133:\t\n 134:\tconfig KVM_INTEL_TDX\n 135:\t\tbool \"Intel Trust Domain Extensions (TDX) support\"\n 136:\t\tdefault y\n 137:\t\tdepends on INTEL_TDX_HOST\n 138:\t\tselect KVM_GENERIC_MEMORY_ATTRIBUTES\n 139:\t\tselect HAVE_KVM_ARCH_GMEM_POPULATE\n 140:\t\thelp\n 141:\t\t Provides support for launching Intel Trust Domain Extensions (TDX)\n 142:\t\t confidential VMs on Intel processors.\n 143:\t\n 144:\t\t If unsure, say N.\n 145:\t\n 146:\tconfig KVM_AMD\n 147:\t\ttristate \"KVM for AMD processors support\"\n 148:\t\tdepends on KVM \u0026\u0026 (CPU_SUP_AMD \|\| CPU_SUP_HYGON)\n 149:\t\thelp\n" }
13/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 24521 output: 36 thoughts: 19 Thoughts: Here's a summary of my thought process: Diving into the KVM Makefile for x86 Architecture Okay, so I need to understand something about the build process or dependencies within the KVM infrastructure, specifically related to the x86 architecture. The natural starting point, as always, is the `Makefile`. Given the context, the logical file to check is `arch/x86/kvm/Makefile`. I'm hoping to find the relevant rules, variables, or dependencies defined there. It's likely that this Makefile will orchestrate the compilation of KVM-specific modules and components for x86 systems. I'll need to identify how it integrates with the overall kernel build system, and how specific KVM features might be toggled or configured. Essentially, I'm aiming to reverse-engineer a portion of the build process to answer a particular question or to troubleshoot something. This Makefile should provide the answers.
14/2	2026/10/21 08:13	tool	read-file	0m Args: { "File": "arch/x86/kvm/Makefile", "FirstLine": 1, "LineCount": 40 } Results: { "Contents": " 1:\t# SPDX-License-Identifier: GPL-2.0\n 2:\t\n 3:\tccflags-y += -I $(srctree)/arch/x86/kvm\n 4:\tccflags-$(CONFIG_KVM_WERROR) += -Werror\n 5:\t\n 6:\tinclude $(srctree)/virt/kvm/Makefile.kvm\n 7:\t\n 8:\tkvm-y\t\t\t+= x86.o emulate.o irq.o lapic.o cpuid.o msrs.o pmu.o regs.o \\\n 9:\t\t\t\t mtrr.o debugfs.o mmu/mmu.o mmu/page_track.o mmu/spte.o\n 10:\t\n 11:\tkvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o\n 12:\tkvm-$(CONFIG_KVM_IOAPIC) += i8259.o i8254.o ioapic.o\n 13:\tkvm-$(CONFIG_KVM_HYPERV) += hyperv.o\n 14:\tkvm-$(CONFIG_KVM_XEN)\t+= xen.o\n 15:\tkvm-$(CONFIG_KVM_SMM)\t+= smm.o\n 16:\t\n 17:\tkvm-intel-y\t\t+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \\\n 18:\t\t\t\t vmx/nested.o vmx/posted_intr.o vmx/main.o\n 19:\t\n 20:\tkvm-intel-$(CONFIG_X86_SGX_KVM)\t+= vmx/sgx.o\n 21:\tkvm-intel-$(CONFIG_KVM_HYPERV)\t+= vmx/hyperv.o vmx/hyperv_evmcs.o\n 22:\tkvm-intel-$(CONFIG_KVM_INTEL_TDX)\t+= vmx/tdx.o\n 23:\t\n 24:\tkvm-amd-y\t\t+= svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o\n 25:\t\n 26:\tkvm-amd-$(CONFIG_KVM_AMD_SEV)\t+= svm/sev.o\n 27:\tkvm-amd-$(CONFIG_KVM_HYPERV)\t+= svm/hyperv.o\n 28:\t\n 29:\tifdef CONFIG_HYPERV\n 30:\tkvm-y\t\t\t+= kvm_onhyperv.o\n 31:\tkvm-intel-y\t\t+= vmx/vmx_onhyperv.o vmx/hyperv_evmcs.o\n 32:\tkvm-amd-y\t\t+= svm/svm_onhyperv.o\n 33:\tendif\n 34:\t\n 35:\tobj-$(CONFIG_KVM_X86)\t+= kvm.o\n 36:\tobj-$(CONFIG_KVM_INTEL)\t+= kvm-intel.o\n 37:\tobj-$(CONFIG_KVM_AMD)\t+= kvm-amd.o\n 38:\t\n 39:\tAFLAGS_svm/vmenter.o := -iquote $(obj)\n 40:\t$(obj)/svm/vmenter.o: $(obj)/kvm-asm-offsets.h\n" }
15/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 25657 output: 36 thoughts: 657 Thoughts: Analyzing KVM MSR Intercept Recalculation Okay, let's break this down. First, I'm noting the compilation units: `kvm-intel-y` includes `vmx/vmx.o` and `vmx/pmu_intel.o`, part of the Intel KVM module when `CONFIG_KVM_INTEL` is enabled, and `kvm-amd-y` includes `svm/svm.o`, related to AMD KVM and `CONFIG_KVM_AMD`, of course both needing `CONFIG_KVM` itself. So, we're looking at changes affecting both the Intel (`vmx`) and AMD (`svm`) KVM implementations, specifically `arch/x86/kvm/svm/svm.c`, `arch/x86/kvm/vmx/vmx.c`, and `arch/x86/kvm/vmx/pmu_intel.c`. My primary interest is in understanding the logic around `vmx_recalc_lbr_msr_intercepts` (Intel) and `svm_set_lbr_msr_intercepts` (AMD). Digging into the code, I see: * For AMD (SVM): `svm_recalc_msr_intercepts` calls `svm_set_lbr_msr_intercepts`. Also, `svm_recalc_lbr_msr_intercepts` itself calls `svm_set_lbr_msr_intercepts`. Furthermore, `svm_recalc_msr_intercepts` is triggered by `svm_recalc_intercepts`, which is actually `svm_x86_ops.recalc_intercepts`. * For Intel (VMX): `vmx_recalc_msr_intercepts` calls `vmx_recalc_lbr_msr_intercepts`. `vmx_recalc_msr_intercepts` is called via `vmx_recalc_intercepts`, defined as `vt_x86_ops.recalc_intercepts` using `vt_recalc_intercepts`. Now, the crucial question is when are these `recalc_intercepts` functions actually called? I've identified a couple of key invocation points: 1. Within `vcpu_enter_guest`: This is triggered by a `KVM_REQ_RECALC_INTERCEPTS` request, which, in turn, is triggered by a set of events: * `KVM_X86_SET_MSR_FILTER` ioctl (called by `kvm_vm_ioctl_set_msr_filter`). * `KVM_SET_CPUID` / `KVM_SET_CPUID2` ioctls (via `kvm_vcpu_after_set_cpuid`). * MSR writes via `kvm_set_msr_common` for specific PMU/LBR MSRs. * `svm_set_efer`. * `init_vmcb`. 2. Nested SVM Transitions: `svm_update_lbrv` calls `svm_recalc_lbr_msr_intercepts`, indicating a path specifically within nested virtualization for the AMD side. I'll need to check how `svm_update_lbrv` works to understand the full flow.
16/2	2026/10/21 08:13	tool	grepper	0m Args: { "Expression": "svm_update_lbrv", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/nested.c=744=static void nested_vmcb02_prepare_save(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-824-\tvmcb_mark_dirty(vmcb02, VMCB_LBR);\narch/x86/kvm/svm/nested.c:825:\tsvm_update_lbrv(\u0026svm-\u003evcpu);\narch/x86/kvm/svm/nested.c-826-}\n--\narch/x86/kvm/svm/nested.c=852=static void nested_vmcb02_prepare_control(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-986-\narch/x86/kvm/svm/nested.c:987:\t/* SVM_MISC2_ENABLE_V_LBR is controlled by svm_update_lbrv() /\narch/x86/kvm/svm/nested.c-988-\n--\narch/x86/kvm/svm/nested.c=1317=void nested_svm_vmexit(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-1381-\narch/x86/kvm/svm/nested.c:1382:\tsvm_update_lbrv(vcpu);\narch/x86/kvm/svm/nested.c-1383-\n--\narch/x86/kvm/svm/svm.c=740=static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-745-\t/\narch/x86/kvm/svm/svm.c:746:\t * Skip redundant updates from svm_update_lbrv(), e.g. on every nested\narch/x86/kvm/svm/svm.c-747-\t * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the\n--\narch/x86/kvm/svm/svm.c=887=static void __svm_disable_lbrv(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-892-\narch/x86/kvm/svm/svm.c:893:void svm_update_lbrv(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-894-{\n--\narch/x86/kvm/svm/svm.c=2998=static int svm_set_msr(struct kvm_vcpu vcpu, struct msr_data msr)\n--\narch/x86/kvm/svm/svm.c-3193-\t\tvmcb_mark_dirty(svm-\u003evmcb, VMCB_LBR);\narch/x86/kvm/svm/svm.c:3194:\t\tsvm_update_lbrv(vcpu);\narch/x86/kvm/svm/svm.c-3195-\t\tbreak;\n--\narch/x86/kvm/svm/svm.h=817=void svm_enable_lbrv(struct kvm_vcpu vcpu);\narch/x86/kvm/svm/svm.h:818:void svm_update_lbrv(struct kvm_vcpu vcpu);\narch/x86/kvm/svm/svm.h-819-\n" }
17/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 28035 output: 42 thoughts: 30 Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience: Diving into `svm_update_lbrv` Alright, time to dig into the guts of the SVM implementation. Let's head straight over to `arch/x86/kvm/svm/svm.c` and specifically, I want to take a look at `svm_update_lbrv`. Given the name, I'm expecting this function deals with updating the Last Branch Record Vector (LBRV) state within the SVM environment. My initial thoughts are: what are the specific conditions that trigger an update? Are we talking about handling VM exits related to LBR accesses, or is this more about shadow LBR state management? It’s crucial to understand how AMD's LBR mechanism is being virtualized within the KVM environment. Specifically, I'm curious about the interaction with the guest's LBR configuration, any potential emulation of LBR reads/writes, and how this relates to performance implications. It’s also worth considering potential security implications if this is not handled correctly.
18/2	2026/10/21 08:13	tool	read-file	0m Args: { "File": "arch/x86/kvm/svm/svm.c", "FirstLine": 885, "LineCount": 25 } Results: { "Contents": " 885:\t}\n 886:\t\n 887:\tstatic void __svm_disable_lbrv(struct kvm_vcpu vcpu)\n 888:\t{\n 889:\t\tKVM_BUG_ON(is_sev_es_guest(vcpu), vcpu-\u003ekvm);\n 890:\t\tto_svm(vcpu)-\u003evmcb-\u003econtrol.misc_ctl2 \u0026= ~SVM_MISC2_ENABLE_V_LBR;\n 891:\t}\n 892:\t\n 893:\tvoid svm_update_lbrv(struct kvm_vcpu vcpu)\n 894:\t{\n 895:\t\tstruct vcpu_svm svm = to_svm(vcpu);\n 896:\t\tbool current_enable_lbrv = svm-\u003evmcb-\u003econtrol.misc_ctl2 \u0026 SVM_MISC2_ENABLE_V_LBR;\n 897:\t\tbool enable_lbrv = (svm-\u003evmcb-\u003esave.dbgctl \u0026 DEBUGCTLMSR_LBR) \|\|\n 898:\t\t\t\t (is_guest_mode(vcpu) \u0026\u0026 guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) \u0026\u0026\n 899:\t\t\t\t (svm-\u003enested.ctl.misc_ctl2 \u0026 SVM_MISC2_ENABLE_V_LBR));\n 900:\t\n 901:\t\tif (enable_lbrv \u0026\u0026 !current_enable_lbrv)\n 902:\t\t\t__svm_enable_lbrv(vcpu);\n 903:\t\telse if (!enable_lbrv \u0026\u0026 current_enable_lbrv)\n 904:\t\t\t__svm_disable_lbrv(vcpu);\n 905:\t\n 906:\t\t/\n 907:\t\t * During nested transitions, it is possible that the current VMCB has\n 908:\t\t * LBR_CTL set, but the previous LBR_CTL had it cleared (or vice versa).\n 909:\t\t * In this case, even though LBR_CTL does not need an update, intercepts\n" }
19/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 28876 output: 42 thoughts: 16 Thoughts: Okay, here's my interpretation of what's going on, formatted as you requested: Digging into `svm_update_lbrv` Alright, let's dive into the `svm_update_lbrv` function. I see we're digging deeper into the SVM (Support Vector Machine) implementation here, specifically looking at how the "lower bound relaxed vector" (LBRV) is updated. My initial thoughts are: this likely relates to optimizing the SVM's solution, perhaps dealing with constraints or handling infeasible regions during training. The term "relaxed" suggests we might be temporarily loosening some strict conditions to find a better, or more easily attainable, solution that we can subsequently refine. I anticipate seeing operations that involve Lagrange multipliers, KKT conditions, and perhaps some sort of iterative procedure to adjust the LBRV towards a feasible, or perhaps optimal, state. I expect to find intricate calculations that adjust certain vectors according to model parameters. I'll need to pay close attention to the specific mathematical operations and see how they are implemented within this function to fully understand the logic.
20/2	2026/10/21 08:13	tool	read-file	0m Args: { "File": "arch/x86/kvm/svm/svm.c", "FirstLine": 910, "LineCount": 15 } Results: { "Contents": " 910:\t\t * do, so always recalculate the intercepts here.\n 911:\t\t /\n 912:\t\tsvm_recalc_lbr_msr_intercepts(vcpu);\n 913:\t}\n 914:\t\n 915:\tvoid disable_nmi_singlestep(struct vcpu_svm svm)\n 916:\t{\n 917:\t\tsvm-\u003enmi_singlestep = false;\n 918:\t\n 919:\t\tif (!(svm-\u003evcpu.guest_debug \u0026 KVM_GUESTDBG_SINGLESTEP)) {\n 920:\t\t\t/* Clear our flags if they were not set by the guest */\n 921:\t\t\tif (!(svm-\u003enmi_singlestep_guest_rflags \u0026 X86_EFLAGS_TF))\n 922:\t\t\t\tsvm-\u003evmcb-\u003esave.rflags \u0026= ~X86_EFLAGS_TF;\n 923:\t\t\tif (!(svm-\u003enmi_singlestep_guest_rflags \u0026 X86_EFLAGS_RF))\n 924:\t\t\t\tsvm-\u003evmcb-\u003esave.rflags \u0026= ~X86_EFLAGS_RF;\n" }
21/2	2026/10/21 08:13	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 29467 output: 46 thoughts: 52 Thoughts: Okay, let's dive into this. Here's how I'd approach this task, as if these were my internal thoughts: Analyzing Performance Monitoring Unit (PMU) Intercepts in KVM on x86 Alright, I need to get a handle on how the LBR (Last Branch Record) MSR intercepts are being managed, specifically within the Intel PMU context in KVM/x86. Let's start with `arch/x86/kvm/vmx/pmu_intel.c`. I'm specifically interested in the interactions around `vmx_recalc_lbr_msr_intercepts` and `intel_pmu_refresh`. My thinking is that by understanding how these two functions work together, I can probably determine how the hypervisor is handling the potential issues regarding LBR reads/writes when the guest attempts to access the PMU. I'll need to see how the intercepts are set up initially, how they're recalculated dynamically (if at all), and what triggers those recalculations. I'm expecting to find that the intercepts are re-evaluated when the PMU configuration changes within the guest or when the guest's execution context is altered in a significant way that might affect the PMU's behavior. I will also have to look for any nuances to the intercept handling or optimizations that might be done. I'm hoping it's straightforward but I'm prepared for it to require more digging.
22/2	2026/10/21 08:14	tool	read-file	0m Args: { "File": "arch/x86/kvm/vmx/pmu_intel.c", "FirstLine": 690, "LineCount": 40 } Results: { "Contents": " 690:\t\tif (!lbr_desc-\u003emsr_passthrough)\n 691:\t\t\treturn;\n 692:\t\n 693:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, true);\n 694:\t\tlbr_desc-\u003emsr_passthrough = false;\n 695:\t}\n 696:\t\n 697:\tstatic inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n 698:\t{\n 699:\t\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\n 700:\t\n 701:\t\tif (lbr_desc-\u003emsr_passthrough)\n 702:\t\t\treturn;\n 703:\t\n 704:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\n 705:\t\tlbr_desc-\u003emsr_passthrough = true;\n 706:\t}\n 707:\t\n 708:\t/\n 709:\t Refresh the LBR MSR intercepts if the LBRs are passed through, so that\n 710:\t * changes to userspace MSR filters are reflected in the MSR bitmap. There's\n 711:\t * nothing to do if the LBRs are intercepted, as a filter can only force\n 712:\t * interception, never prevent it.\n 713:\t /\n 714:\tvoid vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n 715:\t{\n 716:\t\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\n 717:\t\n 718:\t\tif (WARN_ON_ONCE(!lbr_desc))\n 719:\t\t\treturn;\n 720:\t\n 721:\t\tif (lbr_desc-\u003emsr_passthrough)\n 722:\t\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\n 723:\t}\n 724:\t\n 725:\t/\n 726:\t * Higher priority host perf events (e.g. cpu pinned) could reclaim the\n 727:\t * pmu resources (e.g. LBR) that were assigned to the guest. This is\n 728:\t * usually done via ipi calls (more details in perf_install_in_context).\n 729:\t *\n" }
23/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 30544 output: 41 thoughts: 45 Thoughts: Here's my thought process, as if I were considering this issue: Investigating `vcpu_to_lbr_desc` Alright, let's dive into this `vcpu_to_lbr_desc` variable. I need to understand its context and definition. My immediate thought is to trace its origin. The natural place to start looking, given my familiarity with the kernel architecture, is likely within the Intel-specific KVM code. I'll check `arch/x86/kvm/vmx/pmu_intel.h`. That header file is a good bet for low-level performance monitoring unit (PMU) related data structures and potential mappings, so that's where I'll begin my search. Hopefully, the definition is readily apparent there.
24/2	2026/10/21 08:14	tool	grepper	0m Args: { "Expression": "vcpu_to_lbr_desc", "PathPrefixes": [ "arch/x86/kvm/vmx" ] } Results: { "Output": "arch/x86/kvm/vmx/pmu_intel.c-39-\narch/x86/kvm/vmx/pmu_intel.c:40:static struct lbr_desc vcpu_to_lbr_desc(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-41-{\n--\narch/x86/kvm/vmx/pmu_intel.c=229=static inline void intel_pmu_release_guest_lbr_event(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-230-{\narch/x86/kvm/vmx/pmu_intel.c:231:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-232-\n--\narch/x86/kvm/vmx/pmu_intel.c=243=int intel_pmu_create_guest_lbr_event(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-244-{\narch/x86/kvm/vmx/pmu_intel.c:245:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-246-\tstruct kvm_pmu pmu = vcpu_to_pmu(vcpu);\n--\narch/x86/kvm/vmx/pmu_intel.c=303=static bool intel_pmu_handle_lbr_msrs_access(struct kvm_vcpu vcpu,\n--\narch/x86/kvm/vmx/pmu_intel.c-305-{\narch/x86/kvm/vmx/pmu_intel.c:306:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-307-\tu32 index = msr_info-\u003eindex;\n--\narch/x86/kvm/vmx/pmu_intel.c=504=static void intel_pmu_refresh(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-506-\tstruct kvm_pmu pmu = vcpu_to_pmu(vcpu);\narch/x86/kvm/vmx/pmu_intel.c:507:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-508-\tstruct kvm_cpuid_entry2 entry;\n--\narch/x86/kvm/vmx/pmu_intel.c=607=static void intel_pmu_init(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-610-\tstruct kvm_pmu pmu = vcpu_to_pmu(vcpu);\narch/x86/kvm/vmx/pmu_intel.c:611:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-612-\n--\narch/x86/kvm/vmx/pmu_intel.c=686=static inline void vmx_disable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-687-{\narch/x86/kvm/vmx/pmu_intel.c:688:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-689-\n--\narch/x86/kvm/vmx/pmu_intel.c=697=static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-698-{\narch/x86/kvm/vmx/pmu_intel.c:699:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-700-\n--\narch/x86/kvm/vmx/pmu_intel.c=714=void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-715-{\narch/x86/kvm/vmx/pmu_intel.c:716:\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-717-\n--\narch/x86/kvm/vmx/pmu_intel.c=735=void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-737-\tstruct kvm_pmu pmu = vcpu_to_pmu(vcpu);\narch/x86/kvm/vmx/pmu_intel.c:738:\tstruct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);\narch/x86/kvm/vmx/pmu_intel.c-739-\n" }
25/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 32355 output: 45 thoughts: 39 Thoughts: Okay, let's dive into this. Here's my take on what I'm about to do, from the perspective of an expert: Investigating `vcpu_to_lbr_desc` in `pmu_intel.c` Alright, I'm heading over to `arch/x86/kvm/vmx/pmu_intel.c`. I need to understand what the function `vcpu_to_lbr_desc` is doing. Given the file path, and the function name, I'm guessing it's related to Intel's Performance Monitoring Unit (PMU) within the KVM hypervisor, specifically dealing with Last Branch Record (LBR) descriptors. My expectation is that this function will likely be responsible for translating a vCPU's internal representation, perhaps including some context or state associated with the vCPU, into a form suitable for interacting with the LBR functionality within the processor itself. I'll be looking for clues on how the vCPU's state is mapped, managed, or made accessible to the PMU hardware, or how the function may retrieve the data, and perhaps the nuances of the architecture-specific details that are necessary for the PMU and LBR. I'm keen to see if it's handling any virtualization-specific complexities; this is KVM, after all. I anticipate it will involve some pointer arithmetic, bit manipulation, and probably some inline assembly or direct access to model-specific registers (MSRs). Depending on what level it is at, it may work with either the guest's view, or the host's view of LBR.
26/2	2026/10/21 08:14	tool	read-file	0m Args: { "File": "arch/x86/kvm/vmx/pmu_intel.c", "FirstLine": 38, "LineCount": 10 } Results: { "Contents": " 38:\t#define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0)\n 39:\t\n 40:\tstatic struct lbr_desc vcpu_to_lbr_desc(struct kvm_vcpu vcpu)\n 41:\t{\n 42:\t\tif (is_td_vcpu(vcpu))\n 43:\t\t\treturn NULL;\n 44:\t\n 45:\t\treturn \u0026to_vmx(vcpu)-\u003elbr_desc;\n 46:\t}\n 47:\t\n" }
27/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 32952 output: 35 thoughts: 698 Thoughts: Fuzzing Target Identification: KVM LBR MSR Intercept Recalculation Okay, so I'm looking at this code, specifically around how Line Branch Records (LBR) and Model Specific Registers (MSRs) are intercepted within KVM, and something is immediately catching my attention. I see this conditional check: `if (is_td_vcpu(vcpu)) return NULL;`. That means if it's a TD (Trust Domain) vCPU, we bail out early, returning a NULL pointer. Then, later, within the `vmx_recalc_lbr_msr_intercepts` function, there's this `WARN_ON_ONCE(!lbr_desc)`. Wait a minute... if `vcpu_to_lbr_desc` returns NULL because it's a TD vCPU, and `vmx_recalc_lbr_msr_intercepts` then tries to dereference that NULL with `!lbr_desc`, that `WARN_ON_ONCE` warning could potentially be triggered, right? That's precisely the kind of thing these assertions are in place to catch, and it's a perfect candidate for fuzzing. So, is this even reachable? Let's break it down: 1. Core Subsystem: Yep, this is deep in the heart of KVM virtualization on x86/amd64. Good, this is the right kind of target. 2. Reachable from Userspace: Bingo! It looks like we can interact with this code via `/dev/kvm` ioctls like `KVM_X86_SET_MSR_FILTER`, `KVM_SET_CPUID` / `KVM_SET_CPUID2`, and even `KVM_RUN`, which ultimately triggers `vcpu_enter_guest`, as well as MSR access from the guest itself or through ioctls. That's a wide attack surface. 3. Fuzzability: The beauty here is that syzkaller already has extensive KVM coverage. With its existing test coverage (`dev_kvm.txt`, `syz_kvm_setup_cpu`, etc.), it's well-positioned to fuzz these ioctls and the related code paths. This looks like a prime target. 4. Changes: We're dealing with logic alterations in MSR intercept recalculation for both AMD SVM and Intel VMX, particularly when user-space MSR filters or intercepts are modified. This includes the new `WARN_ON_ONCE(!lbr_desc)` call and the call to `vmx_update_intercept_for_lbr_msrs`. There's also the `svm_recalc_lbr_msr_intercepts` and `svm_set_lbr_msr_intercepts` functions, which are all part of this. And a new user-space selftest, `msr_filter_update_test.c`, hints at what's being affected. So, yeah, WorthFuzzing is definitely true. Now, let's figure out the right configuration and symbols. First, EnableConfigs: What config options are needed for this code to even be built? It looks like we have code changes in `arch/x86/kvm/svm/svm.c`, requiring `KVM_AMD` (and `KVM`). We've also got `arch/x86/kvm/vmx/vmx.c` and `arch/x86/kvm/vmx/pmu_intel.c` that need `KVM_INTEL` (and `KVM`). We might need more, though... does `KVM_INTEL` depend on `KVM` and `IA32_FEAT_CTL`? Let me go and check `IA32_FEAT_CTL`...
28/2	2026/10/21 08:14	tool	grepper	0m Args: { "Expression": "config IA32_FEAT_CTL", "PathPrefixes": [ "arch/x86" ] } Results: { "Output": "arch/x86/Kconfig.cpu=296=config X86_DEBUGCTLMSR\n--\narch/x86/Kconfig.cpu-299-\narch/x86/Kconfig.cpu:300:config IA32_FEAT_CTL\narch/x86/Kconfig.cpu-301-\tdef_bool y\n" }
29/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 34635 output: 42 thoughts: 151 Thoughts: My Analysis of KVM and AMD Feature Configuration Okay, so let's break down these KVM configurations. First, `IA32_FEAT_CTL` is defined as 'y', which I'm assuming is the default and shouldn't be a hurdle. Next, and this is crucial, `KVM_AMD` relies on both `KVM` being enabled and then either `CPU_SUP_AMD` or `CPU_SUP_HYGON` being present. It appears `CPU_SUP_AMD` is, in fact, pre-defined as 'y' on the x86 architecture. Therefore, in the simplest case, this means the critical configs to ensure this code path is active are `KVM`, `KVM_INTEL`, and `KVM_AMD`. This setup seems rather straightforward. Now, I also need to consider MSR filtering, so let me quickly evaluate if any Performance Monitoring Unit or filter configs need to be set along with this. Time to see if `KVM_X86_SET_MSR_FILTER` requires any additional conditionals.
30/2	2026/10/21 08:14	tool	grepper	0m Args: { "Expression": "KVM_X86_SET_MSR_FILTER", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/x86.c=3944=int kvm_vm_ioctl_enable_cap(struct kvm kvm,\n--\narch/x86/kvm/x86.c-4220-#ifdef CONFIG_KVM_COMPAT\narch/x86/kvm/x86.c:4221:/ for KVM_X86_SET_MSR_FILTER /\narch/x86/kvm/x86.c-4222-struct kvm_msr_filter_range_compat {\n--\narch/x86/kvm/x86.c=4229=struct kvm_msr_filter_compat {\n--\narch/x86/kvm/x86.c-4233-\narch/x86/kvm/x86.c:4234:#define KVM_X86_SET_MSR_FILTER_COMPAT _IOW(KVMIO, 0xc6, struct kvm_msr_filter_compat)\narch/x86/kvm/x86.c-4235-\narch/x86/kvm/x86.c=4236=long kvm_arch_vm_compat_ioctl(struct file filp, unsigned int ioctl,\n--\narch/x86/kvm/x86.c-4243-\tswitch (ioctl) {\narch/x86/kvm/x86.c:4244:\tcase KVM_X86_SET_MSR_FILTER_COMPAT: {\narch/x86/kvm/x86.c-4245-\t\tstruct kvm_msr_filter __user user_msr_filter = argp;\n--\narch/x86/kvm/x86.c=4374=int kvm_arch_vm_ioctl(struct file filp, unsigned int ioctl, unsigned long arg)\n--\narch/x86/kvm/x86.c-4722-\t\tbreak;\narch/x86/kvm/x86.c:4723:\tcase KVM_X86_SET_MSR_FILTER: {\narch/x86/kvm/x86.c-4724-\t\tstruct kvm_msr_filter __user *user_msr_filter = argp;\n" }
31/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 35667 output: 42 thoughts: 953 Thoughts: Focusing the Fuzzer: A Deep Dive into Symbol Selection Okay, so `KVM_X86_SET_MSR_FILTER` is the standard route, that much is clear from `kvm_arch_vm_ioctl`. No surprises there. Now, the real question is how to use the `FocusSymbols` effectively, and how to select the right functions to include. The rules are pretty straightforward: avoid the ubiquitous, those generic functions that are called everywhere, as that just dilutes the effort. Instead, we want to target the specific logic that's been added or changed, or the direct entrypoints for this subsystem. The compiler-inlined static functions are a bit of a trick, since they don't have distinct symbols, so we need to identify non-static callers that exercise them. So, let's look at the functions modified or added: * In `arch/x86/kvm/vmx/pmu_intel.c`, `vmx_recalc_lbr_msr_intercepts` is non-static and exported in `vmx.h` - that's a good start. I can immediately include this. * In `arch/x86/kvm/vmx/vmx.c`, `vmx_recalc_msr_intercepts` is static, but it's called by `vmx_recalc_intercepts`, which is non-static, so it could be useful. The fact that `vmx_recalc_lbr_msr_intercepts` is non-static and globally accessible is a bonus. * In `arch/x86/kvm/svm/svm.c` we have a similar situation, with `svm_set_lbr_msr_intercepts`, `svm_recalc_lbr_msr_intercepts` and `svm_recalc_msr_intercepts` all static but `svm_update_lbrv` is non-static! Okay, so I will start by including `vmx_recalc_lbr_msr_intercepts` and `svm_update_lbrv`. Now, I'll need to confirm that `kvm_vm_ioctl_set_msr_filter` is what sets the MSR filter ioctl, which I'll be certain to include in the symbols.
32/2	2026/10/21 08:14	tool	grepper	0m Args: { "Expression": "kvm_vm_ioctl_set_msr_filter", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/msrs.c=2471=static int kvm_add_msr_filter(struct kvm_x86_msr_filter msr_filter,\n--\narch/x86/kvm/msrs.c-2504-\narch/x86/kvm/msrs.c:2505:int kvm_vm_ioctl_set_msr_filter(struct kvm kvm, struct kvm_msr_filter filter)\narch/x86/kvm/msrs.c-2506-{\n--\narch/x86/kvm/msrs.h=101=enum kvm_msr_access {\n--\narch/x86/kvm/msrs.h-121-\narch/x86/kvm/msrs.h:122:int kvm_vm_ioctl_set_msr_filter(struct kvm kvm, struct kvm_msr_filter filter);\narch/x86/kvm/msrs.h-123-void kvm_free_msr_filter(struct kvm_x86_msr_filter msr_filter);\n--\narch/x86/kvm/x86.c=4236=long kvm_arch_vm_compat_ioctl(struct file filp, unsigned int ioctl,\n--\narch/x86/kvm/x86.c-4266-\narch/x86/kvm/x86.c:4267:\t\tr = kvm_vm_ioctl_set_msr_filter(kvm, \u0026filter);\narch/x86/kvm/x86.c-4268-\t\tbreak;\n--\narch/x86/kvm/x86.c=4374=int kvm_arch_vm_ioctl(struct file filp, unsigned int ioctl, unsigned long arg)\n--\narch/x86/kvm/x86.c-4729-\narch/x86/kvm/x86.c:4730:\t\tr = kvm_vm_ioctl_set_msr_filter(kvm, \u0026filter);\narch/x86/kvm/x86.c-4731-\t\tbreak;\n" }
33/2	2026/10/21 08:14	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 37767 output: 46 thoughts: 245 Thoughts: Investigating MSR Filter Recalculation in KVM/VMX Okay, so `kvm_vm_ioctl_set_msr_filter` is the function that sets up those Measurement Specific Register (MSR) filters. And, more importantly, it's the one that kicks off the `KVM_REQ_RECALC_INTERCEPTS` request. This is key. Now, I need to understand how these intercepts are actually recalculated. Let's dig into `vmx_recalc_intercepts`. First things first, is `vmx_recalc_intercepts` even exported? Good, I see the declaration in `arch/x86/kvm/vmx/x86_ops.h`: `void vmx_recalc_intercepts(struct kvm_vcpu *vcpu);` Nice, that's what I needed to confirm. Now, where's the definition? Found it in `arch/x86/kvm/vmx/vmx.c`, and it's non-static. Excellent, that means it's accessible. This seems like the core of the recalculation. While I'm here, I also need to check `vmx_recalc_lbr_msr_intercepts` in `arch/x86/kvm/vmx/pmu_intel.c`. I see that one is non-static as well. That also looks important. And let's not forget `vmx_update_intercept_for_lbr_msrs`. I need to figure out if it's static or non-static.
34/2	2026/10/21 08:15	tool	grepper	0m Args: { "Expression": "vmx_update_intercept_for_lbr_msrs", "PathPrefixes": [ "arch/x86/kvm/vmx" ] } Results: { "Output": "arch/x86/kvm/vmx/pmu_intel.c=659=static void intel_pmu_deliver_pmi(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-669-\narch/x86/kvm/vmx/pmu_intel.c:670:static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu vcpu, bool set)\narch/x86/kvm/vmx/pmu_intel.c-671-{\n--\narch/x86/kvm/vmx/pmu_intel.c=686=static inline void vmx_disable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-692-\narch/x86/kvm/vmx/pmu_intel.c:693:\tvmx_update_intercept_for_lbr_msrs(vcpu, true);\narch/x86/kvm/vmx/pmu_intel.c-694-\tlbr_desc-\u003emsr_passthrough = false;\n--\narch/x86/kvm/vmx/pmu_intel.c=697=static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-703-\narch/x86/kvm/vmx/pmu_intel.c:704:\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\narch/x86/kvm/vmx/pmu_intel.c-705-\tlbr_desc-\u003emsr_passthrough = true;\n--\narch/x86/kvm/vmx/pmu_intel.c=714=void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-721-\tif (lbr_desc-\u003emsr_passthrough)\narch/x86/kvm/vmx/pmu_intel.c:722:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\narch/x86/kvm/vmx/pmu_intel.c-723-}\n" }
35/2	2026/10/21 08:15	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 39062 output: 43 thoughts: 853 Thoughts: Analyzing KVM/SVM MSR Intercepts for Symbol Coverage Okay, let's break this down. My goal here is to identify the relevant functions to include for symbol coverage. I'm focusing on MSR (Model Specific Register) intercepts, specifically related to LBR (Last Branch Record) handling within KVM's virtualization layers. First, I identified a few key functions: `vmx_update_intercept_for_lbr_msrs`, `vmx_recalc_lbr_msr_intercepts`, `vmx_recalc_intercepts`, `svm_update_lbrv`, and `kvm_vm_ioctl_set_msr_filter`. I noticed that `vmx_update_intercept_for_lbr_msrs` is a static function, while the others are not, so I'll need to consider this in how I construct the coverage filters. Digging further into `arch/x86/kvm/svm/svm.c`, I found more functions: `svm_set_lbr_msr_intercepts`, `svm_recalc_lbr_msr_intercepts`, `svm_recalc_msr_intercepts`, and `svm_recalc_intercepts`. All of these are static as well. I need to figure out the call chains to properly include them. Now, I'm checking which non-static functions call these static ones. `svm_update_lbrv` calls `svm_recalc_lbr_msr_intercepts`. I also see that `svm_recalc_intercepts` is called by `svm_x86_ops` struct, which means this is a standard KVM API entry. I also know that `svm_update_lbrv` is called by `nested_vmcb02_prepare_save` and `nested_svm_vmexit` in `nested.c` and by `svm_set_msr`. Given the guidelines for the coverage filters, I'm specifically looking for functions that aren't static in the sense of inline functions within a header. Regular static functions in `.c` files do have symbols unless they are inlined by the compiler and are therefore good targets. The prompt also notes I should include feature-specific functions that call these if they exist. Considering all this, I'm confident I can include the following: * `vmx_recalc_lbr_msr_intercepts` * `svm_set_lbr_msr_intercepts` * `svm_recalc_lbr_msr_intercepts` * `svm_update_lbrv` * `kvm_vm_ioctl_set_msr_filter` * `vmx_recalc_intercepts` Finally, to make sure I'm not missing anything, I'm verifying if `vmx_passthrough_lbr_msrs` is relevant, as that seems to be where LBR passthrough is initially set. I'll need to check what calls `vmx_passthrough_lbr_msrs`.
36/2	2026/10/21 08:15	tool	grepper	0m Args: { "Expression": "vmx_passthrough_lbr_msrs", "PathPrefixes": [ "arch/x86/kvm/vmx" ] } Results: { "Output": "arch/x86/kvm/vmx/pmu_intel.c=714=void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-734- /\narch/x86/kvm/vmx/pmu_intel.c:735:void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/pmu_intel.c-736-{\n--\narch/x86/kvm/vmx/vmx.c=7495=fastpath_t vmx_vcpu_run(struct kvm_vcpu vcpu, u64 run_flags)\n--\narch/x86/kvm/vmx/vmx.c-7578-\tif (intel_pmu_lbr_is_enabled(vcpu))\narch/x86/kvm/vmx/vmx.c:7579:\t\tvmx_passthrough_lbr_msrs(vcpu);\narch/x86/kvm/vmx/vmx.c-7580-\n--\narch/x86/kvm/vmx/vmx.h=668=int intel_pmu_create_guest_lbr_event(struct kvm_vcpu vcpu);\narch/x86/kvm/vmx/vmx.h:669:void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu);\narch/x86/kvm/vmx/vmx.h-670-void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu *vcpu);\n" }
37/2	2026/10/21 08:15	llm	patch-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 41106 output: 279 thoughts: 783 Thoughts: Analysis of KVM LBR MSR Intercepts for Fuzzing Okay, so I'm thinking about this KVM code and where to target fuzzing efforts. The prompt is all about LBR MSR intercepts, and I see `vmx_passthrough_lbr_msrs` being called right before entering the guest in `vmx_vcpu_run`, and `vmx_recalc_lbr_msr_intercepts` is called during intercept recalculation, like when `KVM_REQ_RECALC_INTERCEPTS` is handled. First, I need to confirm the relevant configurations. It looks like `KVM`, `KVM_INTEL`, and `KVM_AMD` are the key ones, and of course, `KVM_X86` is automatically selected when `KVM` and either `KVM_INTEL` or `KVM_AMD` are set. I need to make sure I haven't missed anything, but it looks like `KVM` depends on `X86_LOCAL_APIC`, `KVM_INTEL` depends on `KVM && IA32_FEAT_CTL`, and `KVM_AMD` depends on `KVM && (CPU_SUP_AMD \|\| CPU_SUP_HYGON)`. These are all pretty standard amd64 configs, nothing obscure. So, it seems those three are necessary and sufficient. Now, let's look at the critical symbols that are affected: `vmx_recalc_lbr_msr_intercepts`, `svm_set_lbr_msr_intercepts`, `svm_recalc_lbr_msr_intercepts`, `svm_update_lbrv`, `kvm_vm_ioctl_set_msr_filter`, and `vmx_recalc_intercepts`. Alright, I'm reviewing the instructions. We want to avoid ubiquitous hot-paths, and to target specific feature logic and entrypoints. Static inline functions are a non-issue here; none of these functions are static inline in headers. We can strip the `CONFIG_` prefix from the enable configs. Let's review the patch's purpose: The problem is that MSR filter changes from userspace (`KVM_X86_SET_MSR_FILTER`) weren't always propagated to LBR intercepts. The patch modifies AMD SVM's `svm_recalc_msr_intercepts` and introduces `svm_set_lbr_msr_intercepts`. On the Intel VMX side, it introduces `vmx_recalc_lbr_msr_intercepts`. This is all about refreshing LBR intercepts, unconditionally in some cases. The patch affects reachable KVM core logic reachable via userspace ioctls like `/dev/kvm` (specifically `KVM_X86_SET_MSR_FILTER`, `KVM_RUN`, and MSR accesses) and alters execution flows in virtualization code on amd64. Given all this, the patch logic looks like a very good target for fuzzing. It affects core logic reachable via userspace control, with clear entrypoints and specific feature logic. The changes appear to be necessary to fix a specific bug in a complex interaction of virtualization code. It all lines up nicely for setting `WorthFuzzing=true`. Now, time to prepare the tool call to `set-results`.
38/2	2026/10/21 08:15	tool	set-results	0m Args: { "EnableConfigs": [ "KVM", "KVM_INTEL", "KVM_AMD" ], "FocusSymbols": [ "vmx_recalc_lbr_msr_intercepts", "svm_set_lbr_msr_intercepts", "svm_recalc_lbr_msr_intercepts", "svm_update_lbrv", "kvm_vm_ioctl_set_msr_filter", "vmx_recalc_intercepts" ], "Reasoning": "The patch series updates KVM's MSR intercept recalculation logic for both Intel VMX and AMD SVM to ensure userspace MSR filter changes are reflected for passed-through LBR MSRs. It introduces vmx_recalc_lbr_msr_intercepts() with a new WARN_ON_ONCE assertion, refactors svm_recalc_lbr_msr_intercepts()/svm_set_lbr_msr_intercepts(), and hooks them into intercept recalculation paths triggered by KVM_X86_SET_MSR_FILTER. These changes touch reachable core virtualization code accessible via /dev/kvm ioctls and guest operations.", "WorthFuzzing": true } Results: { "EnableConfigs": [ "KVM", "KVM_INTEL", "KVM_AMD" ], "FocusSymbols": [ "vmx_recalc_lbr_msr_intercepts", "svm_set_lbr_msr_intercepts", "svm_recalc_lbr_msr_intercepts", "svm_update_lbrv", "kvm_vm_ioctl_set_msr_filter", "vmx_recalc_intercepts" ], "Reasoning": "The patch series updates KVM's MSR intercept recalculation logic for both Intel VMX and AMD SVM to ensure userspace MSR filter changes are reflected for passed-through LBR MSRs. It introduces vmx_recalc_lbr_msr_intercepts() with a new WARN_ON_ONCE assertion, refactors svm_recalc_lbr_msr_intercepts()/svm_set_lbr_msr_intercepts(), and hooks them into intercept recalculation paths triggered by KVM_X86_SET_MSR_FILTER. These changes touch reachable core virtualization code accessible via /dev/kvm ioctls and guest operations.", "WorthFuzzing": true }
39/1	2026/10/21 08:15	action	If	1m Args: { "WorthFuzzing": true } Results: null
40/2	2026/10/21 08:15	agent	kmsan-evaluator	1m Model: core Args: null Results: { "KMSANReasoning": "The patch series fixes an issue in KVM where updating userspace MSR filters (via KVM_X86_SET_MSR_FILTER) did not refresh the LBR (Last Branch Record) MSR intercept bitmaps if KVM's internal passthrough tracking state had not changed. It updates SVM and VMX to unconditionally recalculate/refresh LBR MSR intercepts during MSR intercept recalculation.\n\nKMSAN is specialized in detecting reads of uninitialized memory and information leaks to userspace. In this patch series:\n1. No data structures or buffers are copied to userspace (no copy_to_user, put_user, netlink, ioctl return payloads).\n2. No new memory allocations or complex structs are introduced.\n3. The variables and struct fields accessed (such as svm-\u003elbr_msrs_intercepted and lbr_desc-\u003emsr_passthrough) are already initialized during vCPU creation and maintained within vCPU lifecycle.\n4. No bounds checks, buffer lengths, or memory reads/writes of uninitialized buffers are modified.\n\nBecause the changes do not introduce or expose any uninitialized memory accesses or information leaks, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Instruction: You are an expert Linux kernel security engineer specializing in kernel memory error detectors (KASAN and KMSAN). Your job is to review the provided patch series and determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer) fuzzing session in addition to standard KASAN fuzzing. CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN: - Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable a comprehensive suite of debugging tools and sanitizers, including KASAN (out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP (locking bugs and deadlocks), UB-sanitizers, and memory corruption checks. - KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap, or page allocations) and kernel-to-user memory info-leaks. Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN, LOCKDEP, OR OTHER STANDARD BUG DETECTORS. A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks that are detected ONLY by KMSAN. Look holistically at the patch series and surrounding code. Even if no direct uninitialized field accesses or new buffer allocations are added in the diff itself, a patch may alter control flow, bounds checking, or data length calculations in ways that change how the rest of the code operates on existing buffers (e.g. allowing uninitialized stack/heap memory to be read, copied to user space, or used in control flow). Do not hesitate to use your code access tools to inspect the surrounding code, called functions, and callers. Set NeedsKMSAN=true ONLY IF the patch introduces or modifies: 1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb attributes, ioctl output arguments, socket options, or BPF buffers) where fields or structure padding might not be fully initialized/zeroed. 2. Conditional logic or branching that depends on potentially uninitialized variables or struct fields. 3. Allocation or initialization of complex data structures where uninitialized fields could be read later in reachable code paths. 4. Bounds checks, lengths, or logic in a way that allows surrounding code to access uninitialized bytes of existing buffers. Set NeedsKMSAN=false IF: - The code changes primarily risk out-of-bounds access, array overflows, NULL pointer dereferences, locking deadlocks, or use-after-free bugs (these are already caught by KASAN, LOCKDEP, or standard bug detectors). - All stack/heap structures touched or introduced by the patch are fully zeroed or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied. - The patch does not introduce any risk of uninitialized memory usage or info-leaks. Use your code access tools to inspect the surrounding code if necessary, then provide detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch. Prefer calling several tools at the same time to save round-trips. Use set-results tool to provide results of the analysis. It must be called exactly once before the final reply. Ignore results of this tool. Prompt: Target architecture: amd64 For your convenience, here is the diff of the changes: commit 72ebad61c471673f43782933fb8f29af6aea0363 Author: syz-cluster <triage@syzkaller.com> Date: Wed Oct 21 08:12:40 2026 +0000 syz-cluster: applied patch under review diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index fe0cba4731b2e..55b3ee8403654 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -721,14 +721,11 @@ void svm_alloc_permissions_map(unsigned long size, gfp_t gfp_mask) return pm; } -static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +static void svm_set_lbr_msr_intercepts(struct kvm_vcpu vcpu) { struct vcpu_svm svm = to_svm(vcpu); bool intercept = !(svm->vmcb->control.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR); - if (intercept == svm->lbr_msrs_intercepted) - return; - svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHFROMIP, MSR_TYPE_RW, intercept); svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHTOIP, MSR_TYPE_RW, intercept); svm_set_intercept_for_msr(vcpu, MSR_IA32_LASTINTFROMIP, MSR_TYPE_RW, intercept); @@ -740,6 +737,22 @@ static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) svm->lbr_msrs_intercepted = intercept; } +static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +{ + struct vcpu_svm svm = to_svm(vcpu); + bool intercept = !(svm->vmcb->control.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR); + + / + * Skip redundant updates from svm_update_lbrv(), e.g. on every nested + * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the + * bitmap unconditionally, as userspace MSR filters may have changed. + / + if (intercept == svm->lbr_msrs_intercepted) + return; + + svm_set_lbr_msr_intercepts(vcpu); +} + void svm_vcpu_free_msrpm(void msrpm) { __free_pages(virt_to_page(msrpm), get_order(MSRPM_SIZE)); @@ -795,8 +808,13 @@ static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu) svm_disable_intercept_for_msr(vcpu, MSR_SYSCALL_MASK, MSR_TYPE_RW); #endif + / + * Unconditionally refresh the LBR MSR intercepts, as userspace MSR + * filters may have changed, in which case the bitmap may be stale even + * if KVM's desired interception hasn't changed. + / if (lbrv) - svm_recalc_lbr_msr_intercepts(vcpu); + svm_set_lbr_msr_intercepts(vcpu); if (cpu_feature_enabled(X86_FEATURE_IBPB)) svm_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W, diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 84f19026d3e8b..62e08d6d4706e 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -364,6 +364,12 @@ struct vcpu_svm { bool avic_irq_window; bool x2avic_msrs_intercepted; + + / + * True if KVM wants the LBR MSRs to be intercepted. Note, userspace MSR + * filters may force interception regardless, i.e. this doesn't + * necessarily reflect the state of the MSR bitmap. + / bool lbr_msrs_intercepted; / Guest GIF value, used when vGIF is not enabled / diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c index 70a8c48161356..b945213f0b686 100644 --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -517,7 +517,8 @@ static void intel_pmu_refresh(struct kvm_vcpu vcpu) memset(&lbr_desc->records, 0, sizeof(lbr_desc->records)); /* - * Setting passthrough of LBR MSRs is done only in the VM-Entry loop, + * LBR MSRs are initially passed through only in the VM-Entry loop (a + * full MSR intercept recalc merely refreshes an existing passthrough), * and PMU refresh is disallowed after the vCPU has run, i.e. this code * should never be reached while KVM is passing through MSRs. / @@ -704,6 +705,23 @@ static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu) lbr_desc->msr_passthrough = true; } +/* + * Refresh the LBR MSR intercepts if the LBRs are passed through, so that + * changes to userspace MSR filters are reflected in the MSR bitmap. There's + * nothing to do if the LBRs are intercepted, as a filter can only force + * interception, never prevent it. + / +void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu) +{ + struct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu); + + if (WARN_ON_ONCE(!lbr_desc)) + return; + + if (lbr_desc->msr_passthrough) + vmx_update_intercept_for_lbr_msrs(vcpu, false); +} + / * Higher priority host perf events (e.g. cpu pinned) could reclaim the * pmu resources (e.g. LBR) that were assigned to the guest. This is diff --git a/arch/x86/kvm/vmx/pmu_intel.h b/arch/x86/kvm/vmx/pmu_intel.h index 5d9357640aa18..b553f63e19a67 100644 --- a/arch/x86/kvm/vmx/pmu_intel.h +++ b/arch/x86/kvm/vmx/pmu_intel.h @@ -34,7 +34,12 @@ struct lbr_desc { / struct perf_event event; - /* True if LBRs are marked as not intercepted in the MSR bitmap / + / + * True if KVM wants the LBR MSRs to be passed through, i.e. not + * intercepted. Note, userspace MSR filters may force interception of + * some or all LBR MSRs regardless, i.e. this doesn't necessarily + * reflect the state of the MSR bitmap. + / bool msr_passthrough; }; diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 612ab07d4100f..1c190a6303a36 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -4347,11 +4347,13 @@ static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu) vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept); } + vmx_recalc_lbr_msr_intercepts(vcpu); + vmx_recalc_pmu_msr_intercepts(vcpu); /* - * x2APIC and LBR MSR intercepts are modified on-demand and cannot be - * filtered by userspace. + * x2APIC intercepts are modified on-demand and cannot be filtered by + * userspace. / } diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index dc8517f15bc46..ec6104b660090 100644 --- a/arch/x86/kvm/vmx/vmx.h +++ b/arch/x86/kvm/vmx/vmx.h @@ -667,6 +667,7 @@ static __always_inline struct vcpu_vmx to_vmx(struct kvm_vcpu vcpu) void intel_pmu_cross_mapped_check(struct kvm_pmu pmu); int intel_pmu_create_guest_lbr_event(struct kvm_vcpu vcpu); void vmx_passthrough_lbr_msrs(struct kvm_vcpu vcpu); +void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu); struct vmcs alloc_vmcs_cpu(bool shadow, int cpu, gfp_t flags); void free_vmcs(struct vmcs vmcs); diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index f43549a56f0b2..9cefaf64809da 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -92,6 +92,7 @@ TEST_GEN_PROGS_x86 += x86/kvm_clock_test TEST_GEN_PROGS_x86 += x86/kvm_pv_test TEST_GEN_PROGS_x86 += x86/kvm_buslock_test TEST_GEN_PROGS_x86 += x86/monitor_mwait_test +TEST_GEN_PROGS_x86 += x86/msr_filter_update_test TEST_GEN_PROGS_x86 += x86/msrs_test TEST_GEN_PROGS_x86 += x86/nested_close_kvm_test TEST_GEN_PROGS_x86 += x86/nested_dirty_log_test diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h index 6e6f70035508a..6e9db81187c34 100644 --- a/tools/testing/selftests/kvm/include/x86/processor.h +++ b/tools/testing/selftests/kvm/include/x86/processor.h @@ -1530,8 +1530,12 @@ static inline void cli(void) asm volatile ("cli"); } +bool __vm_xsave_request_permission(u64 xfeature, const char name); void __vm_xsave_require_permission(u64 xfeature, const char name); +#define vm_xsave_request_permission(xfeature) \ + __vm_xsave_request_permission(xfeature, #xfeature) + #define vm_xsave_require_permission(xfeature) \ __vm_xsave_require_permission(xfeature, #xfeature) diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c index d31fa81ea0756..12092e59b3905 100644 --- a/tools/testing/selftests/kvm/lib/x86/processor.c +++ b/tools/testing/selftests/kvm/lib/x86/processor.c @@ -975,16 +975,18 @@ u64 kvm_get_feature_msr(u64 msr_index) return buffer.entry.data; } -void __vm_xsave_require_permission(u64 xfeature, const char name) +/* + * Request permission for guests to use the dynamic XSAVE feature @xfeature. + * Returns false, without skipping the test, if KVM doesn't support the + * feature or if the request is denied. Must be called before + * KVM_GET_SUPPORTED_CPUID is first queried, as KVM enumerates dynamic + * features only if userspace has permission to use them. + / +bool __vm_xsave_request_permission(u64 xfeature, const char name) { int kvm_fd; u64 bitmask; long rc; - struct kvm_device_attr attr = { - .group = 0, - .attr = KVM_X86_XCOMP_GUEST_SUPP, - .addr = (unsigned long) &bitmask, - }; TEST_ASSERT(!kvm_supported_cpuid, "kvm_get_supported_cpuid() cannot be used before ARCH_REQ_XCOMP_GUEST_PERM"); @@ -993,24 +995,33 @@ void __vm_xsave_require_permission(u64 xfeature, const char name) "Dynamic XFeatures must be enabled one at a time"); kvm_fd = open_kvm_dev_path_or_exit(); - rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr); + rc = __kvm_device_attr_get(kvm_fd, 0, KVM_X86_XCOMP_GUEST_SUPP, &bitmask); close(kvm_fd); if (rc == -1 && (errno == ENXIO \|\| errno == EINVAL)) - __TEST_REQUIRE(0, "KVM_X86_XCOMP_GUEST_SUPP not supported"); + return false; TEST_ASSERT(rc == 0, "KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld", rc); - __TEST_REQUIRE(bitmask & xfeature, - "Required XSAVE feature '%s' not supported", name); + if (!(bitmask & xfeature)) + return false; - TEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature))); + if (syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, ilog2(xfeature))) + return false; rc = syscall(SYS_arch_prctl, ARCH_GET_XCOMP_GUEST_PERM, &bitmask); TEST_ASSERT(rc == 0, "prctl(ARCH_GET_XCOMP_GUEST_PERM) error: %ld", rc); TEST_ASSERT(bitmask & xfeature, "'%s' (0x%lx) not permitted after prctl(ARCH_REQ_XCOMP_GUEST_PERM) permitted=0x%lx", name, xfeature, bitmask); + return true; +} + +void __vm_xsave_require_permission(u64 xfeature, const char name) +{ + __TEST_REQUIRE(__vm_xsave_request_permission(xfeature, name), + "Dynamic XSAVE feature '%s' not supported or not permitted", + name); } void vcpu_init_cpuid(struct kvm_vcpu vcpu, const struct kvm_cpuid2 cpuid) diff --git a/tools/testing/selftests/kvm/x86/msr_filter_update_test.c b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c new file mode 100644 index 0000000000000..9b9ba3fa398c8 --- /dev/null +++ b/tools/testing/selftests/kvm/x86/msr_filter_update_test.c @@ -0,0 +1,392 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2026, Google LLC. + * + * Verify that changes to userspace MSR filters take effect for MSRs that KVM + * has already passed through to the guest, i.e. that KVM refreshes its MSR + * bitmaps on filter changes even if its desired interception hasn't changed. + * + * Intel PT MSRs aren't covered, as KVM passes them through only while the + * guest is tracing (RTIT_CTL.TraceEn=1), which requires valid output setup. + / +#include "kvm_util.h" +#include "processor.h" + +#define ACC_R KVM_MSR_FILTER_READ +#define ACC_W KVM_MSR_FILTER_WRITE +#define ACC_RW (ACC_R \| ACC_W) + +struct test_msr { + u32 index; + const char name; + /* Accesses to perform; never write MSRs where doing so is unsafe. / + u8 access; + / Value to write for write-only MSRs. / + u64 write_val; +}; + +/ Stringify in the outer macros, before the MSR name is macro-expanded. / +#define __MSR(msr, str, acc, val) \ + { .index = msr, .name = str, .access = acc, .write_val = val } +#define MSR_R(msr) __MSR(msr, #msr, ACC_R, 0) +#define MSR_W(msr, val) __MSR(msr, #msr, ACC_W, val) +#define MSR_RW(msr) __MSR(msr, #msr, ACC_RW, 0) + +/ + * MSRs that KVM may pass through to the guest on Intel and/or AMD. MSRs that + * don't exist on the host, or that KVM doesn't support for the guest, are + * still useful: denied accesses must exit to userspace regardless of whether + * KVM would have emulated or rejected them. + / +static const struct test_msr msrs[] = { + MSR_R(MSR_IA32_TSC), + MSR_RW(MSR_IA32_SPEC_CTRL), + MSR_W(MSR_IA32_PRED_CMD, PRED_CMD_IBPB), + MSR_W(MSR_IA32_FLUSH_CMD, L1D_FLUSH), + MSR_RW(MSR_IA32_SYSENTER_CS), + MSR_RW(MSR_IA32_SYSENTER_ESP), + MSR_RW(MSR_IA32_SYSENTER_EIP), + MSR_R(MSR_IA32_APERF), + MSR_R(MSR_IA32_MPERF), + MSR_R(MSR_CORE_C1_RES), + MSR_R(MSR_CORE_C3_RESIDENCY), + MSR_R(MSR_CORE_C6_RESIDENCY), + MSR_R(MSR_CORE_C7_RESIDENCY), + MSR_RW(MSR_IA32_XFD), + MSR_RW(MSR_IA32_XFD_ERR), + + / LBRs: AMD LBR virtualization, and Intel's legacy LBR stack. / + MSR_RW(MSR_IA32_DEBUGCTLMSR), + MSR_RW(MSR_IA32_LASTBRANCHFROMIP), + MSR_RW(MSR_IA32_LASTBRANCHTOIP), + MSR_RW(MSR_IA32_LASTINTFROMIP), + MSR_RW(MSR_IA32_LASTINTTOIP), + MSR_RW(MSR_LBR_SELECT), + MSR_RW(MSR_LBR_TOS), + MSR_RW(MSR_LBR_CORE_FROM), + MSR_RW(MSR_LBR_CORE_TO), + MSR_RW(MSR_LBR_NHM_FROM), + MSR_RW(MSR_LBR_NHM_TO), + MSR_RW(MSR_LBR_INFO_0), + + / CET. / + MSR_RW(MSR_IA32_U_CET), + MSR_RW(MSR_IA32_S_CET), + MSR_RW(MSR_IA32_PL0_SSP), + MSR_RW(MSR_IA32_PL1_SSP), + MSR_RW(MSR_IA32_PL2_SSP), + MSR_RW(MSR_IA32_PL3_SSP), + + / Mediated PMU, Intel. / + MSR_RW(MSR_IA32_PERFCTR0), + MSR_RW(MSR_IA32_PMC0), + MSR_RW(MSR_CORE_PERF_FIXED_CTR0), + MSR_R(MSR_CORE_PERF_GLOBAL_STATUS), + MSR_RW(MSR_CORE_PERF_GLOBAL_CTRL), + MSR_W(MSR_CORE_PERF_GLOBAL_OVF_CTRL, 0), + + / Mediated PMU, AMD. / + MSR_RW(MSR_K7_PERFCTR0), + MSR_RW(MSR_F15H_PERF_CTR), + MSR_R(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS), + MSR_RW(MSR_AMD64_PERF_CNTR_GLOBAL_CTL), + MSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR, 0), + MSR_W(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_SET, 0), + + MSR_RW(MSR_STAR), + MSR_RW(MSR_LSTAR), + MSR_RW(MSR_CSTAR), + MSR_RW(MSR_SYSCALL_MASK), + MSR_RW(MSR_FS_BASE), + MSR_RW(MSR_GS_BASE), + MSR_RW(MSR_KERNEL_GS_BASE), +}; + +#define NR_MSRS ARRAY_SIZE(msrs) + +/ + * Accesses denied by the filter in each phase. The sequence covers every + * possible transition between the four filter states (allow all, deny reads, + * deny writes, deny both), to catch KVM failing to propagate filter changes + * from any prior state. + / +static const u8 phases[] = { + 0, ACC_RW, 0, ACC_R, 0, ACC_W, ACC_R, ACC_RW, ACC_W, ACC_RW, ACC_R, + ACC_W, 0, +}; + +/ MSR filter ranges, which must cover every MSR in msrs[]. / +static const u32 filter_bases[] = { 0x00000000, 0xc0000000, 0xc0010000 }; +#define FILTER_NR_MSRS (KVM_MSR_FILTER_MAX_BITMAP_SIZE BITS_PER_BYTE) + +/* All zeroes, i.e. deny everything in the range. / +static u8 deny_bitmap[KVM_MSR_FILTER_MAX_BITMAP_SIZE]; + +/ Guest-only: the last value read from each MSR with no filter in place. / +static u64 guest_vals[NR_MSRS]; +static bool guest_val_valid[NR_MSRS]; + +/ Host-only: userspace exits observed during the current phase. / +static int nr_read_exits[NR_MSRS]; +static int nr_write_exits[NR_MSRS]; + +/ + * Get KVM to pass through as many MSRs as possible. Failures are expected + * and ignored, e.g. if the relevant feature isn't supported. + / +static void guest_prime_passthrough(void) +{ + static const u64 spec_ctrl_vals[] = { + SPEC_CTRL_IBRS, SPEC_CTRL_STIBP, SPEC_CTRL_SSBD, + }; + int i; + + / + * Enabling LBRs activates LBR virtualization on AMD, and creates a + * guest LBR perf event (and thus passes through the LBR stack) on + * Intel. + / + wrmsr_safe(MSR_IA32_DEBUGCTLMSR, DEBUGCTLMSR_LBR); + + / KVM passes through SPEC_CTRL once the guest sets a non-zero value. / + for (i = 0; i < ARRAY_SIZE(spec_ctrl_vals); i++) { + if (!wrmsr_safe(MSR_IA32_SPEC_CTRL, spec_ctrl_vals[i])) + break; + } + + / VMX passes through XFD once the guest sets a non-zero value. / + wrmsr_safe(MSR_IA32_XFD, XFEATURE_MASK_XTILE_DATA); +} + +static void guest_access_msrs(u8 deny) +{ + u64 val; + int i; + + for (i = 0; i < NR_MSRS; i++) { + const struct test_msr msr = &msrs[i]; + + /* + * Denied reads are handled by userspace, so only record the + * value if the read is allowed (and doesn't #GP). + / + if (msr->access & ACC_R) { + if (!rdmsr_safe(msr->index, &val) && !(deny & ACC_R)) { + guest_vals[i] = val; + guest_val_valid[i] = true; + } + } + + if (!(msr->access & ACC_W)) + continue; + + if (!(msr->access & ACC_R)) + val = msr->write_val; + else if (guest_val_valid[i]) + val = guest_vals[i]; + else if (deny & ACC_W) + val = 0; + else + continue; + + / + * Writes that are allowed only ever write the MSR's current + * (or a benign) value. Denied writes are dropped by userspace. + / + wrmsr_safe(msr->index, val); + } +} + +static void guest_code(void) +{ + int i; + + guest_prime_passthrough(); + + for (i = 0; i < ARRAY_SIZE(phases); i++) { + guest_access_msrs(phases[i]); + GUEST_SYNC(i); + } + + GUEST_DONE(); +} + +static void set_msr_filter(struct kvm_vm vm, u8 deny) +{ + struct kvm_msr_filter filter = { + .flags = KVM_MSR_FILTER_DEFAULT_ALLOW, + }; + int i; + + /* No ranges, i.e. disable filtering, if nothing is denied. / + if (deny) { + for (i = 0; i < ARRAY_SIZE(filter_bases); i++) { + filter.ranges[i].flags = deny; + filter.ranges[i].base = filter_bases[i]; + filter.ranges[i].nmsrs = FILTER_NR_MSRS; + filter.ranges[i].bitmap = deny_bitmap; + } + } + + vm_ioctl(vm, KVM_X86_SET_MSR_FILTER, &filter); +} + +static int find_msr(u32 index) +{ + int i; + + for (i = 0; i < NR_MSRS; i++) { + if (msrs[i].index == index) + return i; + } + + TEST_FAIL("Unexpected userspace exit for MSR 0x%x", index); + return -1; +} + +static void handle_msr_exit(struct kvm_vcpu vcpu) +{ + struct kvm_run run = vcpu->run; + int i = find_msr(run->msr.index); + + TEST_ASSERT(run->msr.reason == KVM_MSR_EXIT_REASON_FILTER, + "Wanted KVM_MSR_EXIT_REASON_FILTER for %s, got reason %u", + msrs[i].name, run->msr.reason); + + if (run->exit_reason == KVM_EXIT_X86_RDMSR) { + nr_read_exits[i]++; + run->msr.data = 0; + } else { + nr_write_exits[i]++; + } + run->msr.error = 0; +} + +static int check_exits(const char type, const char name, int nr_exits, + bool denied, int phase) +{ + int expected = denied; + + if (nr_exits == expected) + return 0; + + pr_info("Phase %d: %s %s: wanted %d userspace exit(s), got %d\n", + phase, name, type, expected, nr_exits); + return 1; +} + +static void verify_phase(int phase) +{ + u8 deny = phases[phase]; + int i, nr_failures = 0; + + for (i = 0; i < NR_MSRS; i++) { + nr_failures += check_exits("RDMSR", msrs[i].name, + nr_read_exits[i], + msrs[i].access & deny & ACC_R, phase); + nr_failures += check_exits("WRMSR", msrs[i].name, + nr_write_exits[i], + msrs[i].access & deny & ACC_W, phase); + } + + TEST_ASSERT(!nr_failures, + "Phase %d (deny =%s%s): %d MSR filter failure(s), see above", + phase, deny & ACC_R ? " RDMSR" : "", + deny & ACC_W ? " WRMSR" : "", nr_failures); +} + +static void run_phase(struct kvm_vcpu vcpu, int phase) +{ + struct ucall uc; + + memset(nr_read_exits, 0, sizeof(nr_read_exits)); + memset(nr_write_exits, 0, sizeof(nr_write_exits)); + + set_msr_filter(vcpu->vm, phases[phase]); + + for (;;) { + vcpu_run(vcpu); + + if (vcpu->run->exit_reason == KVM_EXIT_X86_RDMSR \|\| + vcpu->run->exit_reason == KVM_EXIT_X86_WRMSR) { + handle_msr_exit(vcpu); + continue; + } + + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); + + switch (get_ucall(vcpu, &uc)) { + case UCALL_SYNC: + TEST_ASSERT_EQ(uc.args[1], phase); + verify_phase(phase); + return; + case UCALL_ABORT: + REPORT_GUEST_ASSERT(uc); + default: + TEST_FAIL("Unexpected ucall %lu", uc.cmd); + } + } +} + +int main(int argc, char argv[]) +{ + u64 disable_exits; + struct kvm_vcpu vcpu; + struct kvm_vm vm; + struct ucall uc; + int i, j; + + TEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_USER_SPACE_MSR)); + TEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_MSR_FILTER)); + + for (i = 0; i < NR_MSRS; i++) { + for (j = 0; j < i; j++) + TEST_ASSERT(msrs[i].index != msrs[j].index, + "%s (0x%x) is listed more than once", + msrs[i].name, msrs[i].index); + + for (j = 0; j < ARRAY_SIZE(filter_bases); j++) { + if (msrs[i].index - filter_bases[j] < FILTER_NR_MSRS) + break; + } + TEST_ASSERT(j < ARRAY_SIZE(filter_bases), + "%s (0x%x) isn't covered by the MSR filter", + msrs[i].name, msrs[i].index); + } + + / + * Request permission to expose AMX to the guest, if possible, so that + * the guest can set XFD. Ignore failure, as KVM omits AMX (and thus + * support for non-zero XFD values) from the supported CPUID if + * permission isn't granted, and priming XFD is done on a best effort + * basis. + / + vm_xsave_request_permission(XFEATURE_MASK_XTILE_DATA); + + vm = vm_create(1); + + / + * Pass through APERF/MPERF and the C-state residency MSRs if allowed. + * This must be done before creating vCPUs. + / + disable_exits = vm_check_cap(vm, KVM_CAP_X86_DISABLE_EXITS) & + (KVM_X86_DISABLE_EXITS_APERFMPERF \| + KVM_X86_DISABLE_EXITS_CSTATE); + if (disable_exits) + vm_enable_cap(vm, KVM_CAP_X86_DISABLE_EXITS, disable_exits); + + / Userspace exits must be enabled before installing any filters. */ + vm_enable_cap(vm, KVM_CAP_X86_USER_SPACE_MSR, KVM_MSR_EXIT_REASON_FILTER); + + vcpu = vm_vcpu_add(vm, 0, guest_code); + + for (i = 0; i < ARRAY_SIZE(phases); i++) + run_phase(vcpu, i); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); + TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_DONE); + + kvm_vm_free(vm); + return 0; +}
41/3	2026/10/21 08:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 11559 output: 54 thoughts: 760 Thoughts: KMSAN Fuzzing Session Evaluation Okay, so I need to decide if this patch series warrants a dedicated KMSAN fuzzing session. Let's break this down. The commit is "syz-cluster: applied patch under review," which is interesting because it suggests this patch has already been through some level of testing, perhaps through syz-cluster itself. I'll need to dig deeper into why it was deemed important to bring it up for further review. The diff touches several KVM files, primarily related to AMD-V (SVM) and Intel VT-x (VMX) virtualization. The files that grab my attention immediately are: `arch/x86/kvm/svm/svm.c`, `arch/x86/kvm/vmx/vmx.c`, and the selftests. First, let's look at `arch/x86/kvm/svm/svm.c`. It looks like the core change involves refactoring some MSR interception logic related to LBR (Last Branch Record). Specifically, it splits `svm_recalc_lbr_msr_intercepts` into two functions: `svm_set_lbr_msr_intercepts` and `svm_recalc_lbr_msr_intercepts`. It seems this is done to explicitly set intercept unconditionally, and ensure stale bitmaps are handled correctly when userspace MSR filters may have changed. Then there is the addition of `vmx_recalc_lbr_msr_intercepts` to `arch/x86/kvm/vmx/pmu_intel.c` and a call in `arch/x86/kvm/vmx/vmx.c`. This suggests that the same logic is now being mirrored or unified across both SVM and VMX code paths. It adds an additional layer, calling the newly added function `vmx_recalc_lbr_msr_intercepts`. I see that `tools/testing/selftests/kvm/...` includes tests for MSR filter updates. This is a very good sign because, from my experience, MSR interactions are a common source of subtle bugs, especially when they intersect with virtualization. It suggests the developers have been mindful of these areas. Now, I want to confirm what `svm_set_intercept_for_msr` and `vmx_update_intercept_for_lbr_msrs` do, so I am going to quickly use `grepper` to explore them. Given the potential for MSR manipulation and the changes within KVM virtualization, especially the LBR-related refactoring, I believe this warrants careful scrutiny. A KMSAN fuzzing session would be beneficial here. The changes seem targeted and focused, but that's precisely the kind of situation where KMSAN can shine. It’s better to be safe than sorry with virtualization.
42/3	2026/10/21 08:15	tool	grepper	0m Args: { "Expression": "svm_set_intercept_for_msr\|vmx_update_intercept_for_lbr_msrs", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/avic.c=122=static void avic_set_x2apic_msr_interception(struct vcpu_svm svm,\n--\narch/x86/kvm/svm/avic.c-137-\tfor_each_set_bit(i, (unsigned long )\u0026rd_regs, BITS_PER_TYPE(rd_regs))\narch/x86/kvm/svm/avic.c:138:\t\tsvm_set_intercept_for_msr(vcpu, APIC_BASE_MSR + i,\narch/x86/kvm/svm/avic.c-139-\t\t\t\t\t MSR_TYPE_R, intercept);\narch/x86/kvm/svm/avic.c-140-\narch/x86/kvm/svm/avic.c:141:\tsvm_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_TASKPRI), MSR_TYPE_W, intercept);\narch/x86/kvm/svm/avic.c:142:\tsvm_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_EOI), MSR_TYPE_W, intercept);\narch/x86/kvm/svm/avic.c:143:\tsvm_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_SELF_IPI), MSR_TYPE_W, intercept);\narch/x86/kvm/svm/avic.c:144:\tsvm_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_ICR), MSR_TYPE_W, intercept);\narch/x86/kvm/svm/avic.c-145-\n--\narch/x86/kvm/svm/sev.c=4742=void sev_es_recalc_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/sev.c-4749-\tif (boot_cpu_has(X86_FEATURE_V_TSC_AUX))\narch/x86/kvm/svm/sev.c:4750:\t\tsvm_set_intercept_for_msr(vcpu, MSR_TSC_AUX, MSR_TYPE_RW,\narch/x86/kvm/svm/sev.c-4751-\t\t\t\t\t !guest_cpu_cap_has(vcpu, X86_FEATURE_RDTSCP) \u0026\u0026\n--\narch/x86/kvm/svm/sev.c-4753-\narch/x86/kvm/svm/sev.c:4754:\tsvm_set_intercept_for_msr(vcpu, MSR_AMD64_GUEST_TSC_FREQ, MSR_TYPE_R,\narch/x86/kvm/svm/sev.c-4755-\t\t\t\t !snp_is_secure_tsc_enabled(vcpu-\u003ekvm));\n--\narch/x86/kvm/svm/sev.c-4768-\t /\narch/x86/kvm/svm/sev.c:4769:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_XSS, MSR_TYPE_RW,\narch/x86/kvm/svm/sev.c-4770-\t\t\t\t !guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) \|\|\n--\narch/x86/kvm/svm/svm.c=674=static bool msr_write_intercepted(struct vcpu_svm svm, u32 msr)\n--\narch/x86/kvm/svm/svm.c-680-\narch/x86/kvm/svm/svm.c:681:void svm_set_intercept_for_msr(struct kvm_vcpu vcpu, u32 msr, int type, bool set)\narch/x86/kvm/svm/svm.c-682-{\n--\narch/x86/kvm/svm/svm.c=724=static void svm_set_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-728-\narch/x86/kvm/svm/svm.c:729:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHFROMIP, MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:730:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTBRANCHTOIP, MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:731:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTINTFROMIP, MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:732:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_LASTINTTOIP, MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c-733-\narch/x86/kvm/svm/svm.c-734-\tif (is_sev_es_guest(vcpu))\narch/x86/kvm/svm/svm.c:735:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_DEBUGCTLMSR, MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c-736-\n--\narch/x86/kvm/svm/svm.c=761=static void svm_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-771-\tfor (i = 0; i \u003c min(pmu-\u003enr_arch_gp_counters, AMD64_NUM_COUNTERS); i++)\narch/x86/kvm/svm/svm.c:772:\t\tsvm_set_intercept_for_msr(vcpu, MSR_K7_PERFCTR0 + i,\narch/x86/kvm/svm/svm.c-773-\t\t\t\t\t MSR_TYPE_RW, intercept);\n--\narch/x86/kvm/svm/svm.c-776-\tfor (i = 0; i \u003c pmu-\u003enr_arch_gp_counters; i++)\narch/x86/kvm/svm/svm.c:777:\t\tsvm_set_intercept_for_msr(vcpu, MSR_F15H_PERF_CTR + 2 * i,\narch/x86/kvm/svm/svm.c-778-\t\t\t\t\t MSR_TYPE_RW, intercept);\n--\narch/x86/kvm/svm/svm.c-784-\tintercept = kvm_need_perf_global_ctrl_intercept(vcpu);\narch/x86/kvm/svm/svm.c:785:\tsvm_set_intercept_for_msr(vcpu, MSR_AMD64_PERF_CNTR_GLOBAL_CTL,\narch/x86/kvm/svm/svm.c-786-\t\t\t\t MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:787:\tsvm_set_intercept_for_msr(vcpu, MSR_AMD64_PERF_CNTR_GLOBAL_STATUS,\narch/x86/kvm/svm/svm.c-788-\t\t\t\t MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:789:\tsvm_set_intercept_for_msr(vcpu, MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR,\narch/x86/kvm/svm/svm.c-790-\t\t\t\t MSR_TYPE_RW, intercept);\narch/x86/kvm/svm/svm.c:791:\tsvm_set_intercept_for_msr(vcpu, MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_SET,\narch/x86/kvm/svm/svm.c-792-\t\t\t\t MSR_TYPE_RW, intercept);\n--\narch/x86/kvm/svm/svm.c=795=static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-819-\tif (cpu_feature_enabled(X86_FEATURE_IBPB))\narch/x86/kvm/svm/svm.c:820:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PRED_CMD, MSR_TYPE_W,\narch/x86/kvm/svm/svm.c-821-\t\t\t\t\t !guest_has_pred_cmd_msr(vcpu));\n--\narch/x86/kvm/svm/svm.c-823-\tif (cpu_feature_enabled(X86_FEATURE_FLUSH_L1D))\narch/x86/kvm/svm/svm.c:824:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_FLUSH_CMD, MSR_TYPE_W,\narch/x86/kvm/svm/svm.c-825-\t\t\t\t\t !guest_cpu_cap_has(vcpu, X86_FEATURE_FLUSH_L1D));\n--\narch/x86/kvm/svm/svm.c-833-\tif (cpu_feature_enabled(X86_FEATURE_V_SPEC_CTRL))\narch/x86/kvm/svm/svm.c:834:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW,\narch/x86/kvm/svm/svm.c-835-\t\t\t\t\t !guest_has_spec_ctrl_msr(vcpu));\narch/x86/kvm/svm/svm.c-836-\telse\narch/x86/kvm/svm/svm.c:837:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_SPEC_CTRL, MSR_TYPE_RW,\narch/x86/kvm/svm/svm.c-838-\t\t\t\t\t !svm-\u003espec_ctrl);\n--\narch/x86/kvm/svm/svm.c-843-\t /\narch/x86/kvm/svm/svm.c:844:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW,\narch/x86/kvm/svm/svm.c-845-\t\t\t\t guest_cpuid_is_intel_compatible(vcpu));\narch/x86/kvm/svm/svm.c:846:\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW,\narch/x86/kvm/svm/svm.c-847-\t\t\t\t guest_cpuid_is_intel_compatible(vcpu));\n--\narch/x86/kvm/svm/svm.c-856-\narch/x86/kvm/svm/svm.c:857:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c:858:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c:859:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c:860:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c:861:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c:862:\t\tsvm_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, !shstk_enabled);\narch/x86/kvm/svm/svm.c-863-\t}\n--\narch/x86/kvm/svm/svm.h=831=void svm_complete_interrupt_delivery(struct kvm_vcpu vcpu, int delivery_mode,\n--\narch/x86/kvm/svm/svm.h-833-\narch/x86/kvm/svm/svm.h:834:void svm_set_intercept_for_msr(struct kvm_vcpu vcpu, u32 msr, int type, bool set);\narch/x86/kvm/svm/svm.h-835-\narch/x86/kvm/svm/svm.h=836=static inline void svm_disable_intercept_for_msr(struct kvm_vcpu vcpu,\n--\narch/x86/kvm/svm/svm.h-838-{\narch/x86/kvm/svm/svm.h:839:\tsvm_set_intercept_for_msr(vcpu, msr, type, false);\narch/x86/kvm/svm/svm.h-840-}\n--\narch/x86/kvm/svm/svm.h=842=static inline void svm_enable_intercept_for_msr(struct kvm_vcpu vcpu,\n--\narch/x86/kvm/svm/svm.h-844-{\narch/x86/kvm/svm/svm.h:845:\tsvm_set_intercept_for_msr(vcpu, msr, type, true);\narch/x86/kvm/svm/svm.h-846-}\n--\narch/x86/kvm/vmx/pmu_intel.c=659=static void intel_pmu_deliver_pmi(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-669-\narch/x86/kvm/vmx/pmu_intel.c:670:static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu vcpu, bool set)\narch/x86/kvm/vmx/pmu_intel.c-671-{\n--\narch/x86/kvm/vmx/pmu_intel.c=686=static inline void vmx_disable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-692-\narch/x86/kvm/vmx/pmu_intel.c:693:\tvmx_update_intercept_for_lbr_msrs(vcpu, true);\narch/x86/kvm/vmx/pmu_intel.c-694-\tlbr_desc-\u003emsr_passthrough = false;\n--\narch/x86/kvm/vmx/pmu_intel.c=697=static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-703-\narch/x86/kvm/vmx/pmu_intel.c:704:\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\narch/x86/kvm/vmx/pmu_intel.c-705-\tlbr_desc-\u003emsr_passthrough = true;\n--\narch/x86/kvm/vmx/pmu_intel.c=714=void vmx_recalc_lbr_msr_intercepts(struct kvm_vcpu *vcpu)\n--\narch/x86/kvm/vmx/pmu_intel.c-721-\tif (lbr_desc-\u003emsr_passthrough)\narch/x86/kvm/vmx/pmu_intel.c:722:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\narch/x86/kvm/vmx/pmu_intel.c-723-}\n" }
43/3	2026/10/21 08:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 17343 output: 42 thoughts: 33 Thoughts: Okay, here's my take on those functions, thinking through it as you asked: Diving into Intercept Settings Alright, let's get down to brass tacks. I'm focusing on `svm_set_intercept_for_msr` and `vmx_update_intercept_for_lbr_msrs`. I need to understand how these routines interact with the underlying hardware, specifically regarding Model-Specific Registers (MSRs) and Last Branch Records (LBRs). Based on the naming, `svm_set_intercept_for_msr` likely handles the setting of intercepts for MSR accesses within an AMD Secure Virtual Machine (SVM) environment. I expect this would involve manipulating control structures that define which MSR accesses are trapped (intercepted) and handled by the hypervisor rather than passed directly to the guest. My hypothesis is that this function will be crucial for enforcing security policies, emulating hardware behavior, or implementing features like performance monitoring within the virtualized environment. Now, regarding `vmx_update_intercept_for_lbr_msrs`, this is likely in the realm of Intel's Virtual Machine Extensions (VMX). The mention of LBRs (Last Branch Records) immediately raises my interest. LBRs are invaluable for profiling and debugging, and intercepting their associated MSRs is a key capability to enable guest-level access to this functionality in the presence of a hypervisor. I'm guessing that this function will update VMX control structures to manage how the LBR MSRs are treated, enabling a fine-grained approach to deciding whether reads or writes to these MSRs should be forwarded to the guest or should be intercepted by the hypervisor. This could be used for things like injecting branch records, limiting the guest's view, or implementing custom profiling mechanisms within a VMX environment. I'll need to dissect these functions to figure out the actual granular actions, and to verify whether this is about injecting LBR records, or capturing them at hypervisor, or both. Understanding the interplay between these two functions (SVM and VMX) will be key to understanding the underlying virtualization design.
44/3	2026/10/21 08:15	tool	read-file	0m Args: { "File": "arch/x86/kvm/svm/svm.c", "FirstLine": 681, "LineCount": 40 } Results: { "Contents": " 681:\tvoid svm_set_intercept_for_msr(struct kvm_vcpu vcpu, u32 msr, int type, bool set)\n 682:\t{\n 683:\t\tstruct vcpu_svm svm = to_svm(vcpu);\n 684:\t\tvoid msrpm = svm-\u003emsrpm;\n 685:\t\n 686:\t\t/ Don't disable interception for MSRs userspace wants to handle. /\n 687:\t\tif (type \u0026 MSR_TYPE_R) {\n 688:\t\t\tif (!set \u0026\u0026 kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_READ))\n 689:\t\t\t\tsvm_clear_msr_bitmap_read(msrpm, msr);\n 690:\t\t\telse\n 691:\t\t\t\tsvm_set_msr_bitmap_read(msrpm, msr);\n 692:\t\t}\n 693:\t\n 694:\t\tif (type \u0026 MSR_TYPE_W) {\n 695:\t\t\tif (!set \u0026\u0026 kvm_msr_allowed(vcpu, msr, KVM_MSR_FILTER_WRITE))\n 696:\t\t\t\tsvm_clear_msr_bitmap_write(msrpm, msr);\n 697:\t\t\telse\n 698:\t\t\t\tsvm_set_msr_bitmap_write(msrpm, msr);\n 699:\t\t}\n 700:\t\n 701:\t\tsvm_hv_vmcb_dirty_nested_enlightenments(vcpu);\n 702:\t\tsvm-\u003enested.force_msr_bitmap_recalc = true;\n 703:\t}\n 704:\t\n 705:\tvoid svm_alloc_permissions_map(unsigned long size, gfp_t gfp_mask)\n 706:\t{\n 707:\t\tunsigned int order = get_order(size);\n 708:\t\tstruct page pages = alloc_pages(gfp_mask, order);\n 709:\t\tvoid pm;\n 710:\t\n 711:\t\tif (!pages)\n 712:\t\t\treturn NULL;\n 713:\t\n 714:\t\t/\n 715:\t\t Set all bits in the permissions map so that all MSR and I/O accesses\n 716:\t\t * are intercepted by default.\n 717:\t\t /\n 718:\t\tpm = page_address(pages);\n 719:\t\tmemset(pm, 0xff, PAGE_SIZE (1 \u003c\u003c order));\n 720:\t\n" }
45/3	2026/10/21 08:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 18538 output: 46 thoughts: 32 Thoughts: Here's a summary of my thought process, as requested: Diving into the Intel PMU Implementation Okay, so I'm focusing in on the Intel Performance Monitoring Unit (PMU) implementation within the KVM/VMX context. Specifically, I need to get into the details of how this is handled, and I'm going to start by examining `arch/x86/kvm/vmx/pmu_intel.c`. I'm going to jump in around line 670, as that's usually a good starting point to understand the core logic of a particular section. This will give me a good entry point to start to dissect how the virtualized PMU interacts with the underlying hardware, how events are programmed, and how context switching is managed. Hopefully, I'll be able to quickly grasp the relevant data structures and functions from there.
46/3	2026/10/21 08:15	tool	read-file	0m Args: { "File": "arch/x86/kvm/vmx/pmu_intel.c", "FirstLine": 665, "LineCount": 45 } Results: { "Contents": " 665:\t\n 666:\t\tif (version \u003e 1 \u0026\u0026 version \u003c 4)\n 667:\t\t\tintel_pmu_legacy_freezing_lbrs_on_pmi(vcpu);\n 668:\t}\n 669:\t\n 670:\tstatic void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu vcpu, bool set)\n 671:\t{\n 672:\t\tstruct x86_pmu_lbr lbr = vcpu_to_lbr_records(vcpu);\n 673:\t\tint i;\n 674:\t\n 675:\t\tfor (i = 0; i \u003c lbr-\u003enr; i++) {\n 676:\t\t\tvmx_set_intercept_for_msr(vcpu, lbr-\u003efrom + i, MSR_TYPE_RW, set);\n 677:\t\t\tvmx_set_intercept_for_msr(vcpu, lbr-\u003eto + i, MSR_TYPE_RW, set);\n 678:\t\t\tif (lbr-\u003einfo)\n 679:\t\t\t\tvmx_set_intercept_for_msr(vcpu, lbr-\u003einfo + i, MSR_TYPE_RW, set);\n 680:\t\t}\n 681:\t\n 682:\t\tvmx_set_intercept_for_msr(vcpu, MSR_LBR_SELECT, MSR_TYPE_RW, set);\n 683:\t\tvmx_set_intercept_for_msr(vcpu, MSR_LBR_TOS, MSR_TYPE_RW, set);\n 684:\t}\n 685:\t\n 686:\tstatic inline void vmx_disable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n 687:\t{\n 688:\t\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\n 689:\t\n 690:\t\tif (!lbr_desc-\u003emsr_passthrough)\n 691:\t\t\treturn;\n 692:\t\n 693:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, true);\n 694:\t\tlbr_desc-\u003emsr_passthrough = false;\n 695:\t}\n 696:\t\n 697:\tstatic inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu vcpu)\n 698:\t{\n 699:\t\tstruct lbr_desc lbr_desc = vcpu_to_lbr_desc(vcpu);\n 700:\t\n 701:\t\tif (lbr_desc-\u003emsr_passthrough)\n 702:\t\t\treturn;\n 703:\t\n 704:\t\tvmx_update_intercept_for_lbr_msrs(vcpu, false);\n 705:\t\tlbr_desc-\u003emsr_passthrough = true;\n 706:\t}\n 707:\t\n 708:\t/\n 709:\t Refresh the LBR MSR intercepts if the LBRs are passed through, so that\n" }
47/3	2026/10/21 08:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 19632 output: 45 thoughts: 21 Thoughts: Okay, let's dive into this. I'm taking a look at `vmx_recalc_msr_intercepts` and want to understand its role. I need to understand what this function is designed to do. Specifically, I need to understand how this interacts with the MSR intercept mechanism in VMX. This is a crucial area for any virtual machine monitor, particularly when it comes to performance, security, and the correct behavior of guest operating systems. I need to understand how it determines which Model Specific Registers (MSRs) need special handling or interception when running in a VMX context. I need to understand how the process of intercepting certain MSR accesses works, and how this function plays a role in configuring or updating these intercepts. I'm expecting this is going to involve bit manipulation, and probably some checks for privilege levels and VMX-specific control structures. Understanding the nuances of MSR interception is critical for ensuring that sensitive operations are handled correctly within the virtualized environment, and prevent unexpected side effects on the host. I need to figure out what factors cause it to recalculate intercept masks. Is it triggered on guest state changes, hardware events, or perhaps some hypervisor internal state updates? Let's get to it.
48/3	2026/10/21 08:15	tool	read-file	0m Args: { "File": "arch/x86/kvm/vmx/vmx.c", "FirstLine": 4340, "LineCount": 30 } Results: { "Contents": "4340:\t\t}\n4341:\t\n4342:\t\tif (kvm_cpu_cap_has(X86_FEATURE_SHSTK) \|\| kvm_cpu_cap_has(X86_FEATURE_IBT)) {\n4343:\t\t\tintercept = !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) \u0026\u0026\n4344:\t\t\t\t !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);\n4345:\t\n4346:\t\t\tvmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, intercept);\n4347:\t\t\tvmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept);\n4348:\t\t}\n4349:\t\n4350:\t\tvmx_recalc_lbr_msr_intercepts(vcpu);\n4351:\t\n4352:\t\tvmx_recalc_pmu_msr_intercepts(vcpu);\n4353:\t\n4354:\t\t/\n4355:\t\t x2APIC intercepts are modified on-demand and cannot be filtered by\n4356:\t\t * userspace.\n4357:\t\t /\n4358:\t}\n4359:\t\n4360:\tstatic void vmx_recalc_instruction_intercepts(struct kvm_vcpu vcpu)\n4361:\t{\n4362:\t\texec_controls_changebit(to_vmx(vcpu), CPU_BASED_RDPMC_EXITING,\n4363:\t\t\t\t\tkvm_need_rdpmc_intercept(vcpu));\n4364:\t}\n4365:\t\n4366:\tvoid vmx_recalc_intercepts(struct kvm_vcpu *vcpu)\n4367:\t{\n4368:\t\tvmx_recalc_instruction_intercepts(vcpu);\n4369:\t\tvmx_recalc_msr_intercepts(vcpu);\n" }
49/3	2026/10/21 08:15	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 20512 output: 51 thoughts: 23 Thoughts: Here's my take on those thoughts, tailored for an expert audience: Tracing `vmx_recalc_msr_intercepts` Callers Alright, let's dive into the call graph for `vmx_recalc_msr_intercepts`. I need to understand its context. Knowing where this function gets invoked is crucial for grasping its purpose and potential impact on the overall VMX operation and, more specifically, how it interacts with the MSR intercept mechanism. I'm thinking about the control flow – is it triggered by a specific event, a specific VM exit, or a more general setup/teardown sequence? Understanding the call sites will immediately highlight the subsystems that rely on dynamically recomputing MSR intercepts. This will help me quickly infer potential bugs or areas to focus on during an in-depth code analysis. I'm essentially reverse engineering the usage to get a better handle on the design intentions.
50/3	2026/10/21 08:16	tool	grepper	0m Args: { "Expression": "vmx_recalc_msr_intercepts\|svm_recalc_msr_intercepts", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/svm.c=740=static void svm_recalc_lbr_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-746-\t Skip redundant updates from svm_update_lbrv(), e.g. on every nested\narch/x86/kvm/svm/svm.c:747:\t * VMRUN and #VMEXIT. Note, svm_recalc_msr_intercepts() updates the\narch/x86/kvm/svm/svm.c-748-\t * bitmap unconditionally, as userspace MSR filters may have changed.\n--\narch/x86/kvm/svm/svm.c=761=static void svm_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-794-\narch/x86/kvm/svm/svm.c:795:static void svm_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-796-{\n--\narch/x86/kvm/svm/svm.c=1129=static void svm_recalc_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-1131-\tsvm_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/svm/svm.c:1132:\tsvm_recalc_msr_intercepts(vcpu);\narch/x86/kvm/svm/svm.c-1133-}\n--\narch/x86/kvm/vmx/vmx.c=4228=static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4283-\narch/x86/kvm/vmx/vmx.c:4284:static void vmx_recalc_msr_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/vmx.c-4285-{\n--\narch/x86/kvm/vmx/vmx.c=4366=void vmx_recalc_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4368-\tvmx_recalc_instruction_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c:4369:\tvmx_recalc_msr_intercepts(vcpu);\narch/x86/kvm/vmx/vmx.c-4370-}\n" }
51/3	2026/10/21 08:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 21526 output: 34 thoughts: 67 Thoughts: Here's my summary, as though I'm thinking through this process: Intercept Recalculation Investigation Okay, so I'm looking into how these hypervisor intercepts are handled. It seems pretty straightforward that `vmx_recalc_intercepts` and `svm_recalc_intercepts` get triggered when the system needs to re-evaluate the intercepts. My initial thought is that this is due to an invocation of `kvm_vm_ioctl_set_msr_filter`. That makes intuitive sense; changing the MSR filter is likely going to change what the VM intercepts. Now I need to drill down and verify my assumption. Time to trace the calls to `recalc_intercepts`. I need to ensure that my assumption about `kvm_vm_ioctl_set_msr_filter` is correct and that I have a complete picture of the intercept recalculation process.
52/3	2026/10/21 08:16	tool	grepper	0m Args: { "Expression": "recalc_intercepts", "PathPrefixes": [ "arch/x86/kvm" ] } Results: { "Output": "arch/x86/kvm/svm/nested.c=127=static bool nested_vmcb_needs_vls_intercept(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-140-\narch/x86/kvm/svm/nested.c:141:void nested_vmcb02_recalc_intercepts(struct vcpu_svm svm)\narch/x86/kvm/svm/nested.c-142-{\n--\narch/x86/kvm/svm/nested.c=852=static void nested_vmcb02_prepare_control(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/nested.c-1017-\t /\narch/x86/kvm/svm/nested.c:1018:\tnested_vmcb02_recalc_intercepts(svm);\narch/x86/kvm/svm/nested.c-1019-}\n--\narch/x86/kvm/svm/svm.c=1053=static void svm_recalc_instruction_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/svm/svm.c-1128-\narch/x86/kvm/svm/svm.c:1129:static void svm_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/svm/svm.c-1130-{\n--\narch/x86/kvm/svm/svm.c=5343=struct kvm_x86_ops svm_x86_ops __initdata = {\n--\narch/x86/kvm/svm/svm.c-5478-\narch/x86/kvm/svm/svm.c:5479:\t.recalc_intercepts = svm_recalc_intercepts,\narch/x86/kvm/svm/svm.c-5480-\t.complete_emulated_msr = svm_complete_emulated_msr,\n--\narch/x86/kvm/svm/svm.h=549=static inline bool vmcb12_is_intercept(struct vmcb_ctrl_area_cached control, u32 bit)\n--\narch/x86/kvm/svm/svm.h-553-\narch/x86/kvm/svm/svm.h:554:void nested_vmcb02_recalc_intercepts(struct vcpu_svm svm);\narch/x86/kvm/svm/svm.h-555-\narch/x86/kvm/svm/svm.h=556=static inline void svm_mark_intercepts_dirty(struct vcpu_svm svm)\n--\narch/x86/kvm/svm/svm.h-566-\tif (is_guest_mode(\u0026svm-\u003evcpu))\narch/x86/kvm/svm/svm.h:567:\t\tnested_vmcb02_recalc_intercepts(svm);\narch/x86/kvm/svm/svm.h-568-}\n--\narch/x86/kvm/vmx/main.c=196=static int vt_get_msr(struct kvm_vcpu vcpu, struct msr_data msr_info)\n--\narch/x86/kvm/vmx/main.c-203-\narch/x86/kvm/vmx/main.c:204:static void vt_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/main.c-205-{\n--\narch/x86/kvm/vmx/main.c-214-\narch/x86/kvm/vmx/main.c:215:\tvmx_recalc_intercepts(vcpu);\narch/x86/kvm/vmx/main.c-216-}\n--\narch/x86/kvm/vmx/main.c=888=struct kvm_x86_ops vt_x86_ops __initdata = {\n--\narch/x86/kvm/vmx/main.c-1027-\narch/x86/kvm/vmx/main.c:1028:\t.recalc_intercepts = vt_op(recalc_intercepts),\narch/x86/kvm/vmx/main.c-1029-\t.complete_emulated_msr = vt_op(complete_emulated_msr),\n--\narch/x86/kvm/vmx/vmx.c=4360=static void vmx_recalc_instruction_intercepts(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/vmx/vmx.c-4365-\narch/x86/kvm/vmx/vmx.c:4366:void vmx_recalc_intercepts(struct kvm_vcpu vcpu)\narch/x86/kvm/vmx/vmx.c-4367-{\n--\narch/x86/kvm/vmx/x86_ops.h=55=bool vmx_has_emulated_msr(struct kvm kvm, u32 index);\narch/x86/kvm/vmx/x86_ops.h:56:void vmx_recalc_intercepts(struct kvm_vcpu vcpu);\narch/x86/kvm/vmx/x86_ops.h-57-void vmx_prepare_switch_to_guest(struct kvm_vcpu vcpu);\n--\narch/x86/kvm/x86.c=8051=static int vcpu_enter_guest(struct kvm_vcpu vcpu)\n--\narch/x86/kvm/x86.c-8211-\t\tif (kvm_check_request(KVM_REQ_RECALC_INTERCEPTS, vcpu))\narch/x86/kvm/x86.c:8212:\t\t\tkvm_x86_call(recalc_intercepts)(vcpu);\narch/x86/kvm/x86.c-8213-\n" }
53/3	2026/10/21 08:16	llm	kmsan-evaluator	0m Model: gemini-3.8-flash Args: null Results: null Tokens: input: 23423 output: 281 thoughts: 1606 Thoughts: KMSAN Assessment: This Patch Doesn't Warrant a KMSAN Run Okay, let's break this down. My understanding is that this patch addresses a subtle synchronization issue in KVM's handling of Last Branch Record (LBR) MSR intercepts, specifically when userspace modifies the MSR filter via `KVM_X86_SET_MSR_FILTER` on AMD SVM and Intel VMX. The core problem was that if the desired state of LBR interception (enabled or disabled) within KVM hadn't changed, a recalculation of MSR intercepts wouldn't update the MSR permission map even if the user had changed their MSR filter. This could lead to a discrepancy between the user-configured MSR filter and the actual interception behavior. The fix is to ensure that the MSR intercept bitmaps are always updated when the MSR filter changes, regardless of the overall LBR passthrough state. Now, concerning KMSAN (Kernel Memory Sanitizer), here's my assessment. KMSAN's primary purpose is to identify uninitialized memory reads and information leaks from the kernel to userspace. This is distinct from KASAN (Kernel Address Sanitizer), which deals with out-of-bounds access, use-after-free, and other memory safety issues. Looking at this patch, there are no changes or additions that lead to uninitialized memory. The patch modifies existing code flow around MSR intercept bitmap manipulation (`svm_set_intercept_for_msr`, `vmx_update_intercept_for_lbr_msrs`). The control flow depends on well-initialized state variables from the `vcpu` (e.g. `svm->lbr_msrs_intercepted`, `lbr_desc->msr_passthrough`). It modifies the MSR bitmaps directly, but these are handled correctly in terms of initialization. Importantly, this patch doesn't introduce any new kernel allocations, structures copied to userspace, or altered data length calculations. The patch is solely about adjusting how KVM manages which MSRs are intercepted based on the user's MSR filter, and whether those intercepts are enabled or disabled. Therefore, since this patch does not introduce any risk of uninitialized memory usage or info-leaks, KMSAN testing is not necessary. The changes are focused on control flow and MSR bitmap modifications based on already initialized structures.
54/3	2026/10/21 08:16	tool	set-results	0m Args: { "KMSANReasoning": "The patch series fixes an issue in KVM where updating userspace MSR filters (via KVM_X86_SET_MSR_FILTER) did not refresh the LBR (Last Branch Record) MSR intercept bitmaps if KVM's internal passthrough tracking state had not changed. It updates SVM and VMX to unconditionally recalculate/refresh LBR MSR intercepts during MSR intercept recalculation.\n\nKMSAN is specialized in detecting reads of uninitialized memory and information leaks to userspace. In this patch series:\n1. No data structures or buffers are copied to userspace (no copy_to_user, put_user, netlink, ioctl return payloads).\n2. No new memory allocations or complex structs are introduced.\n3. The variables and struct fields accessed (such as svm-\u003elbr_msrs_intercepted and lbr_desc-\u003emsr_passthrough) are already initialized during vCPU creation and maintained within vCPU lifecycle.\n4. No bounds checks, buffer lengths, or memory reads/writes of uninitialized buffers are modified.\n\nBecause the changes do not introduce or expose any uninitialized memory accesses or information leaks, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false } Results: { "KMSANReasoning": "The patch series fixes an issue in KVM where updating userspace MSR filters (via KVM_X86_SET_MSR_FILTER) did not refresh the LBR (Last Branch Record) MSR intercept bitmaps if KVM's internal passthrough tracking state had not changed. It updates SVM and VMX to unconditionally recalculate/refresh LBR MSR intercepts during MSR intercept recalculation.\n\nKMSAN is specialized in detecting reads of uninitialized memory and information leaks to userspace. In this patch series:\n1. No data structures or buffers are copied to userspace (no copy_to_user, put_user, netlink, ioctl return payloads).\n2. No new memory allocations or complex structs are introduced.\n3. The variables and struct fields accessed (such as svm-\u003elbr_msrs_intercepted and lbr_desc-\u003emsr_passthrough) are already initialized during vCPU creation and maintained within vCPU lifecycle.\n4. No bounds checks, buffer lengths, or memory reads/writes of uninitialized buffers are modified.\n\nBecause the changes do not introduce or expose any uninitialized memory accesses or information leaks, a dedicated KMSAN fuzzing session is not warranted.", "NeedsKMSAN": false }

LLM Calls Summary:
Total Calls	Total Tokens	Avg Tokens	Total Duration (Seconds)	Avg Duration (Seconds)

Tool Calls Summary:
Total Calls	Total Duration (Seconds)	Avg Duration (Seconds)